EAWTH 

1C'.   ri>-c;& 
l&RAftY 


BERKELEY 

LIBRARY 

UNIVERSITY  Of 

CALIFORNIA 


FISHES,   LIVING  AND   FOSSIL 


Columbia  SJnifatsitg  Biological  Series. 

EDITED   BY 

HENRY   FAIRFIELD   OSBORN. 

1     FROM  THE  GREEKS  TO  DARWIN. 

By  Henry  Fairfield  Osborn.  Sc.D.  Princeton. 

2.  AMPHIOXUS  AND  THE  ANCESTRY  OF  THE  VERTEBRATES. 

By  Arthur  Willey,  B.Sc.  Lond.  Univ. 

3.  FISHES,   LIVING  AND   FOSSIL.     An  Introductory  Study, 

By  Bashford  Dean,  Ph.D.  Columbia. 

4.  THE  CELL   IN  DEVELOPMENT  AND   INHERITANCE 

By  Edmund  B.  Wilson,  Ph.D.  J.  H.  U. 


of  DiNiCHTHYS   iNTERMEDius,    NEWBERRY.   in  front 

and  side  views.  X  TV  From  photograph  of  specimen  collected  by  Dr.  William 
Clark,  in  the  Waverly  (Lower  Carboniferous)  of  Ohio,  now  in  the  collection  of 
Columbia  College,  New  York.  (V.  p.  133.) 


COLUMBIA   UNIVERSITY  BIOLOGICAL  SERIES.     III. 


FISHES,   LIVING  AND   FOSSIL 


AN  OUTLINE  OF  THEIR  FORMS  AND 
PROBABLE  RELATIONSHIPS 


BY 


BASHFORD    DEAN,    PH.D. 

INSTRUCTOR  IN  BIOLOGY,  COLUMBIA  COLLEGE,  NEW  YORK  CITY 


Wefo  g«fe 
MACMILLAN    AND    CO. 

AND    LONDON 

1895 
All  rights  reserved 


EARTH 

SCIENCE* 

LIBRARY 


.     COPYRIGHT,  1895, 
t'f  C'  »  '^'i!       I    t\?Yt  1VLA.CMILLAN  AND  CO. 


Set  up  and  electrotyped  August,  1895.      Reprinted   November 
1895. 


MATTHEW  LIBRARY 


XortoooH 

J.  S.  Cashing  &  Co.  —  Berwick  &  Smith. 
Norwood  Mass.  U.S.A. 


MY   FRIEND   AND   TEACHER 

JOHN    STRONG  NEWBERRY 

LATE  PROFESSOR  OF  GEOLOGY  IN 
COLUMBIA  COLLEGE 


942316 


T<ov  8'  ei/vSpoov  £a>an>  TO  TU>V  l^Ovwv  yei/os  ev  o,7r6  roiv 

^>CO/3tCTTat. 

ARISTOTLE,  Z)<?  Animalibus  Historiae,  Lib.  II.,  cap.  xiii. 


PREFACE 


A  KNOWLEDGE  of  Fishes,  living  and  fossil,  is  not  to  be 
included  readily  within  the  limits  of  an  introductory  study. 
In  preparing  the  present  volume  it  has  nevertheless  been 
my  object  to  enable  the  reader  to  obtain  a  convenient 
review  of  the  most  important  forms  of  fishes,  and  of  their 
structural  and  developmental  characters.  I  have  also  en- 
deavoured to  keep  constantly  in  view  the  problems  of  their 
evolution. 

At  the  end  of  the  book  a  series  of  tables  affords  more 
definite  contrasts  of  the  anatomy  and  embryology  of  the 
different  groups  of  fishes.  And  as  an  aid  to  further  study 
has  been  added  a  summarized  bibliography,  including 
especially  the  works  of  the  more  recent  investigators. 

My  sincere  thanks  are  due  to  my  friend  and  colleague, 
Professor  Henry  Fairneld  Osborn,  for  many  suggestions 
during  the  early  preparation  of  the  book,  and  for  the  care 
with  which  he  has  later  revised  the  proof.  I  must  also 
express  my  indebtedness  to  Mr.  Arthur  Smith  Woodward 
of  the  British  Museum  for  his  personal  kindnesses  in 
aiding  my  studies.  My  thanks  are  also  due  to  my  father, 
William  Dean,  for  the  preparation  of  the  index. 

The  figures,  unless  otherwise  stated,  are  from  my 
original  pen  drawings. 

B.  D. 

BIOLOGICAL  LABORATORY  OF  COLUMBIA  COLLEGE, 
May,  1895- 


CONTENTS 


i 

PAGE 

Introductory.  The  form  and  movement  of  Fishes.  Their  classifica- 
tion; geological  distribution;  mode  of  evolution.  The  survival  of 
generalized  forms I 


II 

The   Evolution   of  Structures   characteristic   of  Fishes;   e.g.  (i)  gills, 

(2)  skin  defences,  teeth,  (3)  fins,  and  (4)  sense  organs    ....       14 


III 

The  Lampreys  and  their  Allies.     Their  structures  and  probable  relation- 
ships.    The  Ostracoderms  and  Palseospondylus 57 


IV 

The  Sharks.     Their  plan  of  structure;    prominent   forms,   living   and 

extinct;   their  interrelationships 72 


V 

The  Chimaeroids.     Their  characteristic  structures;   their  representatives 

and  relationships 99 


VI 

The  Lung-fishes.      Their  structures.      Extinct  and  recent  forms.     The 

evolution  of  the  group 116 

xi 


Xii  CONTENTS 


VII 

The  Teleostomes  (i.e.  Ganoids  and  Teleosts).    Typical  members;  their 

structures  and  interrelationships;  their  probable  descent   ....     139 


VIII 

The  Groups  of  Fishes  contrasted  from  the  Standpoint  of  Embryology. 
Their  eggs  and  breeding  habits.  Outlines  of  the  development  of 
Lamprey,  Shark,  Lung-fish,  Ganoid,  and  Teleost.  Their  larval 

development 179 

DERIVATION  OF  NAMES 227 

BIBLIOGRAPHY 231 

EXPLANATORY  TABLES: 

I.     Classification  of  Fishes 8 

II.     Distribution  of  Fishes  in  Geological  Time 9 

III.  Phylogeny  of  Sharks,  Chimaeroids,  Dipnoans       ....  98 

IV.  Phylogeny  of  Teleostomes 166 

V.     Characters  of  Vertebrae,  Fins,  Skull  (Figs.  310-315)     .     .  252 

VI.     Relations  of  Jaws  and  Branchial  Arches  (Figs.  310-315)  .  256 

VII.     Heart  (Figs.  316-325) 260 

VIII.     Gills,  Spiracle,  Gill  rakers  (Figs.  9-12,  326-331)     ...  260 

IX.     Digestive  Tract  (Figs.  326-331) 263 

X.     Swim-Bladder  (Figs.  13-19)  . 264 

XL     Genital  System  (Figs.  331-337) 266 

XII.     Plan  of  Circulation  in  Fishes  (Fig.  338) 269 

XIII.  Excretory  System  (Figs.  331-337) 270 

XIV.  Abdominal  Pores  (Figs.  331-337) 271 

XV.     Central  Nervous  System  (Figs.  339-344) 274 

XVI.     Sense  Organs 276 

XVII.     Integument,  Lateral  line 278 

XVIII.     Developmental  Characters 280 

XIX.     Comparison  of  Phylogenetic  Tables  of  Authors  ....  282 

INDEX , 285 


LIST   OF   FIGURES 


FRONTISPIECE.    Head  of  Dinichthys. 

FIG.  PAGE 

I,  2.  Moving  fishes,   shark   and 

eel 2 

3.  Spanish  mackerel    ....       3 

4.  Front       view      of      Spanish 

mackerel •    .       4 

5-8.  Numerical  lines  of  fishes    .       5 

9-12.  Gills  of  fishes     .     .     .17,259 

13-19.  Air-bladder  .     .     .     .22,  265 

20-31.  Teeth  and  scales     ...     24 

32-38.  Fin  spines 29 

39-43.  Unpaired  fins     ...    32,  33 

44-48.  Caudal  fin 37 

49-54.  Paired  fins 42 

55-60.  Barbels  and  sense  organs  47 
6 1-68.  Mucous  canals  ....  50 
69.  General  anatomy  of  Cyclo- 

stome 58 

.  69  A.  Skeleton  of  lamprey  ...  58 
70-72  A-D.  Bdellostoma,  Myx- 

ine,  Petromyzon      .     .    60,  61 

73.  Palaeospondylus 65 

74.  Pteraspis 66 

75.  Palaeaspis 66 

76.  77.  Plates  of  Pteraspis  ...     66 

78,  79.  Cephalaspis 66 

So-82.  Pterichthys 68 

83.  General  anatomy  of  shark      .      73 
.84.  Skeleton  of  shark    .     .     .75,  255 

85.  Vertebrae  of  shark   ....  76 

86.  86  A.  Cladoselache  ....  79 
86  B.  Teeth  of  Cladoselache    .     .  80 

87.  Acanthodes 81 

88.  Acanthodes,  shagreen .     .     .  81 
88  A.  Acanthodes,  teeth     ...  82 
£.  Climatius 82 


FIG.  PAGE 

90.  Pleuracanthus 83 

90  A.  Teeth  of  Pleuracanthus      .  84 

90  B.  Head  roof  of  Pleuracanthus  84 

91.  Cestracion 85 

92.  Chlamydoselache  ....  87 

93.  Heptanchus 88 

94.  Squalus 89 

95.  Alopias 89 

96.  Lamna 90 

96  A.  Cetorhinus 90 

968.   Lsemargus 91 

97.  Squatina 91 

98.  98  A.  Pristis 92 

99.  Pristiophorus 93 

100.  Rhinobatis 93 

101.  Raja 94 

102.  Torpedo 95 

IO2A.  Dicerobatis       (Cephalop- 

tera) 96 

103.  Shark  phylogeny  ....  98 

104.  General  anatomy  of  Chimaera  100 

105.  Skeleton  of  Chimaera       .     .  102 
105  A.  Ischyodus 104 

1 06.  Myriacanthus 105 

io6A.  Squaloraja 105 

io6B,  c.  Derm  plates  of  Myria- 
canthus    105 

107-112.  Dental  plates  of  Chimse- 

roids 106 

1 1 3-1 1 6  A.  Spines  and  claspers 

of  Chimaeroids  ....  107 

117.  Harriotta 108 

118.  Callorhynchus 109 

119.  Chimaera no 

1 20.  Chimaera,  young    .     .     .     .ill 

121.  General  anatomy  of  lung-fish  117 


XIV 


LIST   OF  FIGURES 


FIG.-  PAGE 

122.  Skeleton  of  lung-fish  .     .     .119 
1 22  A.  Jaws  and  skull  of  Protop- 

terus 120 

123.  Dipterus 121 

124.  Derm  bones  of  head  of  Dip- 

terus   121 

125.  125  A.  Jaws  of  Dipterus  .     .   121 

126.  Phaneropleuron     .     .     .     .122 

127.  Ceratodus 123 

128.  Skeleton  of  Ceratodus     .     .123 

1 28  A.  Skull  of  Ceratodus   .     .     .124 

129.  Lepidosiren 125 

1 29  A.  Protopterus 126 

130.  Coccosteus 131 

131.  Coccosteus,  dorsal  view  .     .132 

132.  Coccosteus,  ventral     .     .     .132 

133.  Dinichthys 133 

134-137.  Dinichthys,  dorsal  view  134 
138-144.  Mandibles  of  Arthrodi- 

rans 137 

145.  General  anatomy  of  Teleost  140 

146.  Skeleton  of  Teleost    .     .     .   142 

147.  Skeleton  of  Ganoid    .     .     .  144 

148.  Polypterus 148 

149.  Polypterus,  head  of  young   .   148 

150.  Calamoichthys 150 

151.  Gyroptychius 151 

152.  Osteolepis 151 

153.  Holoptychius 151 

154.  Eusthenopteron     .     .     .     .152 

155.  Coelacanthus 153 

156.  Diplurus 154 

156  A.  Undina 154 

157.  Lepidosteus 155 

158.  Elonichthys 156 

159.  Eurynotus 156 

160.  Cheirodus 157 

161.  Semionotus 157 

162.  Aspidorhynchus     .     .     .     .158 

163.  Microdon 158 

164.  Palseoniscus 159 

165.  Acipenser 160 

1 65  A.  Chondrosteus      .     .     .     .161 

1 66.  Scaphirhynchus     .     .     .     .162 


1 66  A.  Psephurus 162 

i66B.   Polyodon 163 

167.  Amia 163 

1 68.  Amia,  gular  region     .      .     .   164 

169.  Caturus 164 

170.  Leptolepis 165 

171.  Megalurus 165 

1 71  A.  Phylogeny   of   the   Teleo- 

stomes 166 

172-174.  Deep-sea  fishes  .     .     .168 

175.  Fierasfer 169 

176.  Carassius 170 

177.  Amiurus 171 

178.  Callichthys 172 

179.  Mormyrus 172 

180.  Anguilla 173 

181.  Perca 173 

182.  Gadus 174 

183.  Pseudopleuronectes    .     .     .175 

184.  Chilomycterus 176 

1 84  A.  Lagocephalus      .     .     .     .176 

185.  Hippocampus 177 

1 85  A.  Syngnathus 178 

186-199.  Eggs  of  fishes     .     .     .181 
200-215.  Development    of    lam- 
prey     189 

216-230.  Development  of  shark  .    194 
231-248.  Development   of   lung- 
fish     199,  201 

249-268.  Development  of  Ganoid  203 
269-283.  Development  of  Teleost  208 
284-289.  Larval  sharks  .  .  .216 
290-295.  Larval  lung-fishes  .  .219 
296-302.  Larval  sturgeons .  .  .  222 
303-309.  Larval  Teleosts  .  .  .  224 
310-315.  Skulls,  jaws,  and  bran- 
chial arches  ....  254 
316-325.  Heart  and  conus  arte- 

riosus 258 

326-331.  Digestive  tracts   .     .     .   262 
332-337.  Urinogenital  ducts  and 

openings 267 

338.  Blood-vessels  of  shark     .     .   268 
339-344-  Brain 272 


FISHES   IN   GENERA^ 

INTRODUCTION 


FISHES,  defined  in  a  popular  way,  are  back-boned  ani- 
mals, gill-breathing,  cold-blooded,  and  provided  with  fins. 
It  is  in  their  conditions  of  living  that  they  have  differed 
widely  from  the  remaining  groups  of  vertebrates.  Aquatic 
life  has  stamped  them  in  a  common  mould  and  has  pre- 
scribed the  laws  which  direct  and  limit  their  evolution ;  it 
has  compressed  their  head,  trunk,  and  tail  into  a  spindle- 
like  form ;  it  has  given  them  an  easy  and  rapid  motion, 
enabling  them  to  cleave  the  water  like  a  rounded  wedge. 
It  has  made  their  mode  of  movement  one  of  undulation, 
causing  the  sides  of  the  fish  to  contract  rhythmically, 
thrusting  the  animal  forward.  A  clear  idea  of  this  mode 
of  motion  is  to  be  obtained  from  a  series  of  photographs  of 
a  swimming  fish  (Figs.  1-2)  taken  at  successive  instants : 
thus  in  the  case  of  the  shark  (Fig.  i)  the  undulation  of 
the  body  may  be  traced  from  the  head  region  backward, 
passing  along  the  sides  of  the  body,  and  may  be  seen  to 
actually  disappear  at  the  tip  of  the  tail.  It  is  the  press- 
ure of  the  fish's  body  against  the  water  enclosed  in  these 
incurved  places  which  causes  the  forward  movement. 

The  density  of  the  living  medium  of  fishes  exerts  upon 
them  a  mechanical  influence ;  they  are,  so  to  say,  balanced 
in  water,  free  to  proceed  in  all  planes  of  direction,  poised 


2  FISHES  IN  GENERAL 

with  the  utmost  accuracy,  enabled  to  rise  to  the  surface  or 
sink  readily  into  deep  water.  A  special  organ,  the  'air-,' 
or  'swim-bladder/  has  even  been  acquired  by  the  majority 
of  living  fishes,  which,  whatever  may  have  been  its  origin 
or  accessory  functions  (v.  p.  21),  has  certainly  to  an  extraor- 


Figs,  i  and  2.  —  Movement  of  fishes, —  shark  and  eel.     (After  MAREY.) 

•dinary  degree  the  power  of  rendering  the  specific  gravity 
of  the  fish  the  same  as  that  of  the  surrounding  water. 

In  an  example  of  a  swift-swimming  fish  some  of  the 
most  striking  peculiarities  of  the  aquatic  form  may  be 
seen.  The  Spanish  mackerel,  Scomberomorus  (Fig.  3), 
shows  admirably  a  stout  spindle-like  outline  ;  its  entire  sur- 


FORM  AND  FINS 


face  is  accurately  rounded, 
and  there  appear  no  irregu- 
lar points  which  could  re- 
tard the  forward  motion  of 
the  fish.  Even  in  the 
wedge-shaped  head  the 
conical  surface  has  been 
made  more  perfect  by  the 
tightly  fitting  rims  of  the 
jaws,  by  the  smoothly 
closed  gill  shields,  and  by 
the  eyes'  accurate  adjust- 
ment to  the  head's  curva- 
ture. Viewed  from  in  front 
(Fig.  4)  the  fish's  outline 
appears  as  a  perfect  ellipse, 
and  seems  surprisingly 
small  in  size :  the  fins,  which 
appear  so  prominent  a  feat- 
ure in  profile,  can  now 
be  hardly  distinguished ; 
above  and  below  they  form 
keels,  sharp  and  thin.  In 
side  view  the  vertical  or 
unpaired  fins  are  seen  sur- 
rounding the  hinder  region 
of  the  body :  they  resolve 
themselves  into  dorsal  (D\ 
anal  (A),  and  caudal  (C) 
elements ;  the  former  are 
low  and  stout,  elastic  in  pig.  3.  _Type  of  swift  swimming  fish 

their  firm  CUtwater  margin,   Spanish  mackerel,  Scomberomorus  macula- 
j         ,  tus  (Mitch.),  J.  &G.    X  i.     (After  GOODE 

deeply  notched  and  inter-  in  u.  s.  F.  c.) 


4  FISHES  IN  GENERAL 

rupted  posteriorly,  where  useless  elements  have  been  dis- 
carded ;  the  caudal  is  'broadly  forked,  stout  in  its  support- 
ing rays,  strong  in  power  of  propulsion.  At  its  sides  a 
remarkable  ridge  has  been  developed,  functioning  as  a 
horizontal  keel  (R)  and  preventing  the  stroke  of  the  cau- 
dal from  varying  from  the  vertical  plane. 
The  lateral,  or  paired  fins,  pectoral  and  ven- 
tral (P  and  F),  may  rotate  outward  and 
arrange  themselves  in  the  line  of  the  fish's 
motion,  so  that  in  a  somewhat  horizontal 
plane  they  may,  like  the  unpaired  fins,  func- 
tion as  keels.  When  thus  erected,  the 
paired  fins  present  a  firm  anterior  margin 
which 'serves  as  a  cutwater.  While  thus 
somewhat  similar  in  function  to  the  vertical 
fins,  the  ventrals  and  especially  the  pecto- 

Fig.4.-Front  .       r 

view   of  Spanish  rals  may  acquire  additional  uses  :  they  may 
serve  as  delicate  balancers,  or  may  aid  in 
guiding  or  arresting  the  fish's  motions. 

In  further  conformity  to  aquatic  needs,  the  entire  sur- 
face of  the  fish  is  notably  slime  covered,  and  although 
perfectly  armoured  by  plates  and  scales,  yet  presents  no 
point  of  resistance  to  forward  motion.  An  internal  balance, 
moreover,  has  been  effected  between  the  supporting,  vis- 
ceral and  muscular  parts :  the  firm  vertebral  axis  acquires 
its  central  position,  and  at  its  anterior  end  the  head  struct- 
ures form  a  compact,  wedge-like  mass  :  the  body  muscles 
which  give  the  fish  its  form-contour  thin  away  on  the  ven- 
tral side,  permitting  in  the  region  between  the  head  and 
the  anal  fin  the  space  occupied  by  the  closely  compacted 
viscera :  respiratory  organs  occupy  a  restricted  space  on 
either  side  of  the  gullet ;  the  heart  and  its  arterial  trunk 
are  implanted  closely  in  the  throat  in  the  median  ventral 


NUMERICAL  LINES 


line ;  the  dorsal  blood-vessel  takes  its  position  immediately 
below  the  vertebral  axis,  and  the  air-bladder  in  the  most 
dorsal  part  of  the  abdominal  cavity. 


FIG.  5 


Figs.  5-8.  —  Numerical  lines  of  fishes  and  cetaceans.  The  "entering  angle" 
begins  at  the  snout-tip  at  the  right,  and  extends  as  far  as  the  vertical  dotted  line 
(36  %,  about,  of  the  entire  length)  ;  the  "  run  "  then  begins  and  is  continued  to  the 
body  terminal.  5.  Striped  porpoise,  Phocaena  lineata.  6.  Spanish  mackerel 
(Cuban),  Scomberomorus  cavalla.  7.  Humpback  whale,  Megaptera  longimana. 
8.  Striped  bass,  Labrax  lineatus.  (All  figures  after  PARSONS.) 

In  acquiring  this  perfect  outward  symmetry  it  is  inter- 
esting to  note  that  the  forms  of  fishes  may  be  said  to  have 
actually  evolved  the  practical  solution  of  the  most  theoretical 
problems  of  curves  and  displacement  in  relation  to  sub- 


6  FISHES  IN  GENERAL 

marine  motion.  A  study  of  the  "  lines  "  of  typical  fishes  by 
naval  engineers  *  has  led  to  some  most  interesting  results 
as  to  the  uniformity  of  their  mathematical  "  normals."  It 
is  found,  for  example,  that  the  "entering  angles  "  of  many 
and  very  different  fishes  are  surprisingly  similar  (Figs.  6 
and  8)  :  they  thus  terminate  regularly  (at  the  plane  of  the 
greatest  cross-section  of  the  body)  at  36  per  cent  of  the 
fish's  total  length;  and  the  curves  of  the  "run"  (i.e.  of 
the  hinder  part  of  the  trunk,  from  the  plane  of  the  great- 
est cross-section  to  the  body  terminal),  similar  for  all,  are 
smooth  hollow  curves,  which  in  the  forward  motion  of  the 
fish  permit  the  passage  of  the  displaced  water. 

It  would  be  unreasonable  to  doubt  that  the  fish  form  is 
adapted  to  the  mechanical  needs  of  its  environment,  even 
if  there  existed  no  further  evidence  than  that  of  the  meta- 
morphoses of  aquatic  mammals.  Many  of  these  have 
shown  so  complete  an  adaptation  to  water-living  that  it  is 
scarcely  remarkable  that  they  were  early  included  among 
fishes.  And  it  is  of  further  interest  that  there  exist 
transitional  forms  between  the  land-living  mammals  on 
the  one  hand  and  the  cetaceans  on  the  other.  In  the 
Seal  it  is  but  the  initial  step  in  the  transformation  that 
has  taken  place ;  the  head  and  body  have  become  bluntly 
tapering,  the  hind  legs  displaced  backward,  the  foot  and 
hand  webbed,  the  hair  adapted  to  submerged  locomotion. 
A  further  stage  in  the  acquisition  of  the  fish-like  form  is 
shown  in  the  Dugong  and  Manatee.  And  finally  in  the 
Dolphin  and  Whale  (Figs.  5  and  7)  have  been  actually 
attained  the  numerical  lines  of  fishes  (cf.  Figs.  6  and  8). 
In  these  cases,  the  mechanical  conditions  of  aquatic  living 
have  produced  their  result  only  at  the  greatest  cost,  — 

*  '88.  Parsons,  Displacement  and  Area  Curves  of  Fishes,  Trans.  Am.  Soc. 
Mech.  Engineers. 


CLASSIFICATION  j 

enormous  structural  and  physiological  changes  had  of 
necessity  to  have  been  attained.  The  frame  of  the 
head  and  trunk  has  become  moulded  as  in  the  fish's 
form,  contours  have  been  elaborately  filled  out  and 
rounded,  median  dermal  keels  developed,  vein  valves  lost, 
and  the  legs  transformed  into  fin-like  appendages. 

The  form  of  the  fish  is  accordingly  to  be  looked  upon  as 
cast  in  a  more  or  less  common  mould  by  its  environment. 
Its  internal  structures,  as  in  the  cetacean,  are  also  ob- 
served  to  be  modified  in  accordance  with  its  external  form. 
This  is  a  factor  in  the  evolution  of  fishes  which  appears 
in  every  group  and  sub-group.  And  it  has  ever  stood  in 
the  way  of  classifying  them  satisfactorily  according  to 
their  kinships. 

"Fishes,"  used  as  a  popular  term,  may  include  Lam- 
preys, Sharks,  Chimaeroids,  Lung-fishes,  and  "Modern 
Fishes"  (Teleostomes),  —  the  major  groups  to  be  dis- 
cussed in  the  present  book.  But  the  relative  position  of 
each  of  these  divisions  must  at  present  remain  more  or 
less  doubtful.  The  group  of  the  Lampreys  is  certainly 
widely  removed  from  the  remaining  ones,  standing  mid- 
way between  the  simplest  chordate,  Amphioxus,  and  the 
true  fishes :  it  is  usually  given  a  rank  co-ordinate  with 
either  of  these,  and,  in  fact,  with  all  other  groups 
of  vertebrates,  taken  collectively.  Sharks,  Chimaeroids, 
Teleostomes,  may  be  taken  to  represent  true  fishes  ;  and 
each  might  be  assigned  co-ordinate  rank,  although  geneti- 
cally the  Chimaeroids  are  certainly  far  more  closely  allied 
to  the  Sharks  than  are  the  Teleostomes.  The  Lung-fishes, 
as  a  widely  divergent  group,  appear,  as  W.  N.  Parker  has 
suggested,  to  be  reasonably  entitled  to  a  rank  equivalent 
to  that  of  the  three  groups  of  true  fishes  taken  together. 


3  FISHES  IN  GENERAL 

The  present  writer  has,  however,  retained  in  the  main 
the  classification  of  Smith  Woodward,  in  which  Fishes 
(Pisces)  is  looked  upon  as  a  class,  and  is  made  to  include 
as  sub-classes,  (I.)  Sharks,  (II.)  Chimaeroids,  (III.)  Lung- 
fishes,  and  (IV.)  Teleostomes.  A  tabular  grouping  of  the 
fishes  is  shown  below.  And  on  the  opposite  page  their 
geological  distribution  is  indicated. 

TABLE   I 

A   CLASSIFICATION   OF  FISHES 

Type:  CHORDATA  (VERTEBRATES). 

Class:   Marsipobranchii,  Lampreys,  Pal&ospondylus,   Hag,   Lam- 
prey, Ostracoderms . 
Class :  Pisces  (True  Fishes) . 

I.   Sub-class:  ELASMOBRANCHII,  Sharks  and  Rays. 

Order:  Pleuropterygii  (Dean),  Cladoselachids  (Dean). 
"        Ickthyotomi  (Cope),  Pleuracanthids . 
"         Selachii,  Sharks  and  Rays. 
II.   Sub-class:  HOLOCEPHALI,  Chimaeroids,  Spook-fishes. 

Order:  Chimaeroidei,     Squaloraiids,     Myriacanthids, 
Chimaerids. 

III.  Sub-class:  DIPNOI,  Lung-fishes. 

Order:  Sirenoidei,   Dipterids,   Phaneropleurids,    Cte- 

nodonts,  Lepidosirenids. 
"          ?     Arthrodira,  Coccosteids,  Mylostomids. 

IV.  Sub-class:    TELEOSTOMI,    Ganoids    and    Bony    Fishes 

(Teleosts) . 
Order:  Crossopterygii,      Holoptychiids,      Osteolepids, 

Onychodonts,  Ccelacanthids . 
"         Actinopterygii, 

Sub-order:  Chondrostei  (Ganoids),  Palceoniscoids, 

Sturgeons,  Garpikes,  Amioids. 
"  Teleocephali,  recent  Bony  Fishes  (Tel- 

eosts). 

NOTE. —  The  groups  italicized  are  represented  only  in  fossil  forms. 
The  derivations  of  the  scientific  names  are  given  on  pp.  227-230. 


GEOLOGICAL  DISTRIBUTION 


TABLE    II 
THE   DISTRIBUTION   OF    FISHES   IN   GEOLOGICAL    TIME 

The  geological  distribution  of  the  prominent  groups  of  fishes  as  here  shown  is  in  the  main 
as  given  by  Zittel  (Palaeontologie:  Fische).  The  varying  thickness  of  the  lines  denotes  ap- 
proximately increase  or  diminution  in  the  number  of  existing  genera. 


Silurian. 

Devonian. 

Carbonif- 
erous. 

Permian. 

0 

H 

.g 

3 
•—  > 

Creta- 
ceous. 

1 

Miocene. 

Pliocene. 

Recent. 

MarsipobrancMi. 

Cyclostomes    .     .     . 
PPteraspids  .     .'    .     . 
PCephalaspids   .     .     . 
Palaeospondylus  . 
PPterichthids     .     .     . 

Elasmobranchii. 
Cladoselache    .     .     . 
Acanthodians  .     .     . 
Pleuracanthids     .     . 

1 
1 

• 

1 
1 

m 

•• 

•• 

KB 

• 
™ 

• 
•• 

un 

•™ 

MMB 

Cestracionts     .     .     . 

Recent    sharks     (in- 
cluding Notidanids) 

Rhinobatus       .     .     . 

Pristis      

Pristiophorus  .     .     . 

Chimaeroids   .... 

Dipnoans. 
Dipterus      .... 
Ceratodus    .... 

1 

- 

- 

~ 

IBBB 

am 

M~ 

MW 

Teleostomes. 

Crossopterygians  .     - 

Acipenseroids  . 

Perches    and     Bery- 
cids 

Siluroids      .... 

Gadoids    and    other 
Teleosts    .... 

- 

— 

— 

P 

I0  FISHES  IN  GENERAL 

Fishes  hold  an  important  place  in  the  history  of  back- 
boned animals  :  their  group  is  the  largest  and  most  widely 
distributed :  its  fossil  members  are  by  far  the  earliest 
of  known  chordates ;  and  among  its  living  representa- 
tives are  forms  which  are  believed  to  closely  resemble 
the  ancestral  vertebrate. 

The  different  groups  of  fishes  appear  especially  favour- 
able for  comparative  study.  Their  recent  forms  are  gen- 
erally well  understood,  both  structurally  and  developmen- 
tally ;  while  a  vast  number  of  extinct  fishes  has  been 
preserved  to  serve  as  a  check,  as  well  as  an  aid,  to  theoret- 
ical investigation. 

The  remarkable  permanence  of  the  different  types  of 
fishes  seems  a  striking  proof  of  how  unchanging  must 
have  ever  been  the  conditions  of  aquatic  living.  From  as 
early  as  the  Devonian  times  there  have  been  living  mem- 
bers of  the  four  sub-classes  of  existing  fishes, — Sharks,  Chi- 
masroids,  Dipnoans,  and  Teleostomes.  Even  their  ancient 
sub-groups  (orders  and  sub-orders)  usually  present  surviving 
members ;  while,  on  the  other  hand,  there  is  but  a  single 
group  of  any  structural  importance  that  has  been  evolved 
during  the  lapse  of  ages, — the  sub-order  of  Bony  Fishes. 
There  are  many  instances  in  which  even  the  very  types  of 
living  fishes  are  known  to  be  of  remarkable  antiquity : 
thus  the  genus  of  the  Port  Jackson  Shark,  Cestracion 
(Fig.  91),  is  known  to  have  been  represented  early  in  the 
Mesozoic;  the  Australian  Lung-fish,  Ceratodus  (Fig.  127), 
dates  back  to  Liassic  times;*  the  Frilled  Shark,  C/tlamy- 
doselache  (Fig.  92),  though  not  of  a  palaeozoic  genus,  as 
formerly  supposed  (Cope),  must  at  least  be  regarded  as 
closely  akin  to  the  Sharks  of  the  Silurian. 

*  Cf.,  however,  Smith  Woodward,  The  Fossil  Fishes  of  the  Hawkesbury 
Series  at  Gosford.  Memoirs  of  the  Geol.  Surv.  of  N.  S.  W.  Pal.  No.  4,  1890. 


MODE   OF  EVOLUTION  U 

The  evolution  of  groups  of  fishes  must,  accordingly, 
have  taken  place  during  only  the  longest  periods  of  time. 
Their  aquatic  life  has  evidently  been  unfavourable  to  deep- 
seated  structural  changes,  or  at  least  has  not  permitted 
these  to  be  perpetuated.  Recent  fishes  have  diverged  in 
but  minor  regards  from  their  ancestors  of  the  Coal  Meas- 
ures. Within  the  same  duration  of  time,  on  the  other 
hand,  terrestrial  vertebrates  have  not  only  arisen,  but  have 
been  widely  differentiated.  Among  land-living  forms  the 
amphibians,  reptiles,  birds,  and  mammals  have  been 
evolved,  and  have  given  rise  to  more  than  sixty  orders. 

The  evolution  of  fishes  has  been  confined  to  a  note- 
worthy degree  within  rigid  and  unshifting  bounds ;  their 
living  medium,  with  its  mechanical  effects  upon  fish-like 
forms  and  structures,  has  for  ages  been  almost  constant 
in  its  conditions ;  its  changes  of  temperature  and  density 
and  currents  have  rarely  been  more  than  of  local  im- 
portance, and  have  influenced  but  little  the  survival  of 
genera  and  species  widely  distributed  ;  its  changes,  more- 
over, in  the  normal  supply  of  food  organisms,  cannot  be 
looked  upon  as  noteworthy.  Aquatic  life  has  built  few 
of  the  direct  barriers  to  survival,  within  which  the  ter- 
restrial forms  appear  to  have  been  evolved  by  the  keenest 
competition. 

It  is  not,  accordingly,  remarkable  that  in  their  descent 
fishes  are  known  to  have  retained  their  tribal  features,  and 
to  have  varied  from  each  other  only  in  details  of  structure. 
Their  evolution  is  to  be  traced  in  diverging  characters 
that  prove  rarely  more  than  of  family  value ;  one  form, 
as  an  example,  may  have  become  adapted  for  an  active 
and  predatory  life,  evolving  stronger  organs  of  progression, 
stouter  armouring,  and  more  trenchant  teeth ;  another, 
closely  akin  in  general  structures,  may  have  acquired  more 


I2  FISHES  IN  GENERAL 

sluggish  habits,  larger  or  greatly  diminished  size,  and  degen- 
erate characters  in  its  dermal  investiture,  teeth,  and  organs 
of  sense  or  progression.  The  flowering  out  of  a  series  of 
fish  families  seems  to  have  characterized  every  geological 
age,  leaving  its  clearest  imprint  on  the  forms  which  were 
then  most  abundant.  The  variety  that  to-day  maintains 
among  the  'families  of  Bony  Fishes  is  thus  known  to 
have  been  paralleled  among  the  Carboniferous  Sharks,  the 
Mesozoic  Chimaeroids,  and  the  Palaeozoic  Lung-fishes  and 
Teleostomes.  Their  environment  has  retained  their  gen- 
eral characters,  while  modelling  them  anew  into  forms 
armoured  or  scaleless,  predatory  or  defenceless,  great, 
small,  heavy,  stout,  sluggish,  light,  slender,  blunt,  taper- 
ing, depressed. 

When  members  of  any  group  of  fishes  became  extinct, 
those  appear  to  have  been  the  first  to  perish  which  were 
the  possessors  of  the  greatest  number  of  widely  modified 
or  specialized  structures.  Those,  for  example,  whose  teeth 
were  adapted  for  a  particular  kind  of  food,  or  whose 
motions  were  hampered  by  ponderous  size  or  weighty 
armouring,  were  the  first  to  perish  in  the  struggle  for 
existence ;  on  the  other  hand,  the  forms  that  most  nearly 
retained  the  ancestral  or  tribal  characters  —  that  is,  those 
whose  structures  were  in  every  way  least  extreme  —  were 
naturally  the  best  fitted  to  survive.  Thus  generalised 
fishes  should  be  considered  those  of  medium  size,  medium 
defences,  medium  powers  of  progression,  omnivorous  feed- 
ing habits,  and  wide  distribution  :  and  these  might  be  re- 
garded as  having  provided  the  staples  of  survival  in  every 
branch  of  descent. 

Aquatic  living  has  not  demanded  wide  divergence  from 
the  ancestral  stem,  and  the  divergent  forms  which  may 
culminate  in  a  profusion  of  families,  genera,  and  species, 


EVOLUTION  !3 

do  not  appear  to  be  again  productive  of  more  generalized 
groups.  In  all  lines  of  descent  specialized  forms  do  not 
appear  to  regain  by  regression  or  degeneration  the  potential 
characters  of  their  ancestral  condition.  A  generalized  form 
is  like  potter's  clay,  plastic  in  the  hands  of  nature,  readily 
to  be  converted  into  a  needed  kind  of  cup  or  vase  ;  but 
when  thus  specialized  may  never  resume  unaltered  its 
ancestral  condition :  the  clay  survives ;  the  cup  perishes. 


II 


THE    EVOLUTION    OF    STRUCTURES    CHAR- 
ACTERISTIC   OF    FISHES 

IT  will  be  the  object  of  the  present  chapter  to  review 
the  gradations  which  occur  in  some  of  the  characteristic 
structures  of  fishes  and  to  follow  in  some  degree  the 
mode  of  their  evolution.  We  may  thus  review  the  con- 
ditions of  the  (i)  gills,  (2)  skin  defences  (including  teeth), 
(3)  fins,  and  (4)  sense  organs. 

The  structures  of  the  immediate  ancestor  of  the  fishes 
cannot  be  definitely  inferred :  the  form,  however,  must 
have  been  elongate  and  transversely  jointed,  for  this  con- 
dition seems  to  have  existed  remotely  before  fishes  —  in 
the  broadest  sense  —  had  become  evolved.  This  segmen- 
tation, or  metamerism,  of  the  vertebrate  body  is  best  shown 
among  water-living  forms,  sometimes  indeed  in  so  perfect 
a  way  as  to  suggest  the  jointed  condition  of  an  earth-worm. 

The  segmented  body  of  the  eel-shaped  Lamprey,  shown 
in  section  in  Fig.  69,  illustrates  an  interesting  condition 
of  vertebrate  metamerism.  Its  entire  body,  from  the 
head  region  to  the  base  of  the  tail,  is  composed  of  drum- 
like  segments  which  closely  correspond  to  one  another 
in  size  and  in  component  structures.  Each  segment 
thus  resembles  its  neighbours  in  its  equal  portions  of  the 
vertebral  column,  digestive  tract,  nerve  tube,  muscle 
plates  and  blood  canal,  and  in  the  arrangement  of  these 
parts  with  reference  to  bilateral  symmetry.  Motion  in 
this  form  requires  no  more  of  each  segment  than  that  its 


EVOLUTION  OF  STRUCTURES  ^ 

sides  contract  alternately  to  produce  a  rhythmical  wave 
passing  along  the  entire  series  of  segments  and  giving  the 
trunk  an  undulatory  movement. 

Should  this  elongate  body  now  acquire  a  more  fish-like 
form,  in  attaining,  for  example,  the  power  of  more  rapid 
movement,  it  is  obvious  that  this  simple  type  of  meta- 
merism would  undergo  a  series  of  changes.  Every  change 
of  outward  form  would  be  reflected  on  the  parts  not  only 
of  each,  but  of  all  segments  in  their  common  relationships. 
To  perform  more  perfectly  the  functions  of  their  location, 
adjacent  segments  might  become  enlarged,  folded,  or 
blended,  and  cause  the  most  puzzling  complications  of 
their  component  structures.  One  region  of  the  body  might 
thus  appear  to  develop  at  the  expense  of  another,  as  in  the 
evolution  of  fin  structures  (cf.  pp.  32-44),  where  a  vertical 
fin  fold,  representing  the  sum  of  the  dorsal  and  ventral  out- 
growths of  the  hinder  body  segments,  becomes  reduced  to 
the  lappet-like  dorsal  and  ventral  fins ;  the  intervening 
substance  of  the  fin  web  becoming  drawn  to  the  points 
where  greater  rigidity  is  required. 

The  simple  metameral  character  of  the  lamprey  acquires 
an  especial  interest  when  the  different  groups  of  fishes  are 
examined ;  for  it  is  found  that  all  exhibit  clearly  body 
segments  and  segmental  structures  in  the  most  varied 
stages  of  complexity.  To  trace  metamerism  seems,  accord- 
ingly, a  mode  of  determining  to  what  degree  the  differ- 
ent groups  have  diverged  from  a  common  stem ;  and  to 
compare  the  sums  of  the  archaic  metameral  characters  in 
the  different  types  of  fishes  may  perhaps  be  looked  upon 
as  one  of  the  safest  aids  in  determining  their  genetic  posi- 
tion. From  the  conditions  of  segmentation  the  lampreys 
must  certainly  be  given  a  lowly  rank ;  even  with  due  allow- 
ance for  degeneration  of  structures  they  are  clearly  more 


jg  EVOLUTION  OF  STRUCTURES 

primitive  than  the  most  archaic  sharks :  while,  on  the 
other  hand,  to  the  metameral  type  of  the  sharks  may  the 
structures  of  the  remaining  groups  of  fishes  be  best  referred. 

i.   AQUATIC  BREATHING 

Respiration  in  fishes  is  developed  on  the  primitive  chor- 
date  plan  of  ejecting  water  through  gill  slits  perforating 
the  throat  wall.  The  water  taken  in  by  the  mouth  is  rich 
in  absorbed  air,  and,  as  it  passes  out,  is  well  calculated  to 
oxygenate  the  blood  suffusing  the  sides  of  the  gill  slits. 

Among  the  earliest  chordates  there  seems  evidence 
that  the  gill  openings  of  the  gullet  were  arranged  with 
reference  to  some  form  of  primitive  segmentation.  Per- 
haps they  occurred  as  well  in  the  region  of  the  mid-diges- 
tive tract,  before  their  location  became  restricted  to  the 
gullet.  There  has  been  as  yet,  however,  little  satisfactory 
evidence  *  as  to  the  number  or  conditions  of  the  gill  slits 
in  very  primitive  forms.  In  Amphioxus  the  gill  arrange- 
ment seems  clearly  a  most  specialized  one :  its  adult  con- 
dition presents  an  atrium  and  an  elaborate  branchial 
basket,!  which  could  hardly  have  occurred  in  the  lowly 
ancestral  chordate.  Its  early  larva,  however,  is  known,  to 
possess  (but  in  a  condition  of  assymmetry)  but  a  few  gill 
slits  (seven  to  nine)  from  which  the  many  openings  of  the 
adult  branchial  basket  take  their  origin,  —  a  developmental 
stage  which  most  closely  and  most  interestingly  suggests 
the  conditions  of  higher  forms. 

*  It  has  generally  been  inferred  that  the  immediate  ancestors  of  fishes  had 
not  many  gill  slits,  probably  not  more  than  eight  or  nine.  A  Liassic  shark,  a 
Cestraciont,  Hybodus  (p.  85),  is  known  to  have  had  but  five;  a  Permian  Pleu- 
racanthid,  as  in  the  recent  Heptanchus,  seven  (p.  88) ;  the  Lower  Carbonifer- 
ous Cladoselache  probably  seven. 

t  Cf.  Vol.  II,  of  this  series.  Willey,  Amphioxus  and  Other  Ancestors  of  th& 
Chordates. 


g 


Figs.  9-12.  — Arrangement  of  gills  of  Bdellostoma  (9),  Myxine  (10),  Shark  (n),  and 
Teleost  (12).     In  each  figure  the  surface  of  the  head  region  is  shown  at  the  left. 

B.  Barbels.  BD.  Outer  duct  from  gill  chamber,  BS.  BO.  Common  opening  of  outer 
ducts  from  gill  chambers.  BS.  Branchial  sac,  or  gill  chamber.  BS '.  Branchial  sac,  sec- 
tioned so  as  to  show  the  folds  of  its  lining  membrane.  G.  Lining  membrane  of  gullet. 
GB.  Gill  bar,  supporting  vessels  and  filaments  of  gills.  GC.  Outer  opening  of  gill  cleft. 
GF.  Gill  filament.  GR.  Gill  rakers.  G  V.  Vessels  of  gill.  J,  J '.  Upper  and  lower  jaw. 
M.  Mouth  opening.  N,N'.  Anterior  and  posterior  opening  of  nasal  chamber.  OP.  Oper- 
cuhim.  SP.  Spiracle.  ST.  Tendinous  septum  between  anterior  and  posterior  gill  filaments. 
*  Denotes  the  inner  branchial  opening ;  -» ,  the  direction  of  the  water  current. 
C  17 


jg  AQUATIC  BREATHING 

In  the  singular  group  of  lampreys  and  slime  eels  (Mar- 
sipobranchs,  v.  p.  57),  the  segmental  arrangement  of  the 
gills  seems  of  a  primitive  pattern.  In  the  Californian 
Myxinoid  (p.  59)  the  slits  are  as  numerous  as  thirteen  and 
fourteen  on  either  side,  each  opening  directly  from  the 
gullet  to  the  neck  surface  (Fig.  9,  G,  *,  BS\  BD).  In  the 
lamprey  the  conditions  are  similar,  but  the  number  of  gill 
slits  is  reduced  to  seven.  In  Myxine  (Fig.  10,  G,  BS\  BD, 
BO)  the  outer  portions  of  the  canals  becoming  produced 
taij-ward  have  merged  in  a  single  pore  (Fig.  71  *).  In  these 
forfrfs  each  gill  canal  has  become  dilated  at  one  point  of 
its  course,  and  in  this  sac-like  portion  the  blood-suffused 
tissues  have  grouped  themselves  into  leaf-like  plates  (gill 
filaments,  or  lamellae,  BS')  to  increase  their  surface  of 
contact  with  the  out-passing  water.  The  dilating  power 
of  this  gill  sac  has  then  become  specialized  so  that  even 
should  the  animal's  mouth  be  closed,  water  for  respiration 
could  be  drawn  in  through  the  canal's  outer  opening : 
from  this  acquired  function  the  elaboration  of  bran- 
chial muscles  and  a  supporting  framework  of  cartilage 
(branchial  basket,  Fig.  69  A,  BB)  may  have  taken  its 
origin. 

Among  fishes  proper  many  stages  in  the  evolution  of 
gill  organs  are  represented.  They  show  altogether  a 
marked  advance  over  the  conditions  of  Fig.  9.  There 
has  been  a  general  tendency  to  press  closely  together  the 
gill  pouches  and  to  elaborate  into  thinner  and  larger 
lamellae  the  blood-suffused  tissue.  In  this  process  the 
gill  chamber  has  become  slit-like,  bearing  gill  lamellae  only 
on  its  front  and  rear  margins ;  its  supporting  tissue  has  con- 
solidated into  stout  vertical  gill  bars,  the  gill  structures  in 
general,  becoming  more  highly  perfected,  tending  to  recede 
from  the  surface.  These  conditions  may  best  be  illustrated 


GILL    CHARACTERS  IC; 

by  contrasting  the  highly  modified  gill  apparatus  of  a  bony 
fish  with  the  more  archaic  type  of  the  shark. 

In  the  sharks  (p.  73)  the  gill  slits  pierce  separately 
the  throat  wall,  as  in  the  lamprey,  and  thus  retain  their 
primitive  segmental  arrangement  (Fig.  11).  Their  number 
is  usually  five  on  either  side,  but  in  an  archaic  form  (Hep- 
tanchus,  p.  88)  may  be  increased  to  seven.  Above  and 
in  front  of  the  line  of  gill  slits  occurs  a  small  opening 
leading  into  the  gullet,  the  spiracle  (SP).  This,  though 
at  present  possessing  but  few  gill  lamellae,  and  therefore 
of  little  respiratory  value,  was  doubtless  quite  like  its 
neighbours  before  its  gill-supporting  tissue  became  of  value 
in  suspending  the  lower  jaw.  It  may  now  aid  the  mouth 
opening  in  admitting  water  to  the  gills.  At  the  left  of 
the  figure  (Fig.  11),  the  narrow  slit-like  openings  of  the 
gill  clefts  are  seen  at  GC:  at  the  right,  where  the  upper 
portion  of  the  head  has  been  removed,  the  gill  lamellae 
are  shown  at  GF\  the  tissue  intervening  between  the 
gill  pouches  is  reduced  to  a  thin  tendinous  septum,  57", 
at  whose  inner  rim  is  the  cartilaginous  gill  arch  or  bar, 
GB,  supporting  the  branchial  vessels,  G  V. 

In  the  gill  region  of  a  bony  fish  (Fig.  12)  a  number  of 
modified  characters  are  now  evident :  the  spiracle  has 
become  obliterated;  the  number  of  gill  bars  reduced  — 
in  one  form  but  two  on  either  side  remaining.  These 
have  become  closely  pressed  together,  and  bent  backward, 
receding  from  the  surface  of  the  head  :  their  gill  lamellae 
have  become  larger  and  more  numerous,  their  intervening 
septum,  ST,  reduced  in  size.  The  gills  no  longer  open 
separately  at  the  surface,  but  into  an  outer  branchial 
chamber  formed  and  protected  by  a  large  overlapping 
scale,  or  opercle,  OP.  This  shield-like  organ  is  hinged 
at  its  anterior  margin  and  opens  or  shuts  rhythmically  as 


20  GILL    CHARACTERS 

the  throat  muscles  draw  in  or  eject  the  water  used  in 
respiration.  On  the  gullet  wall,  the  gill  bars,  now  seen 
to  be  closely  drawn  together,  have  acquired  marginal 
outgrowths,  or  gill  rakers,  GR,  which  form  an  inter- 
locking screen  across  the  gill  openings  and  prevent  the 
escape  of  food  organisms.  So  perfect  may  this  apparatus 
become  that  the  opening  and  closing  gill  bars  may  retain 
even  microscopic  life.* 

Between  the  conditions  of  Figs,  n  and  12  there  occur 
many  transitional  forms. 

To  protect  the  gill  region,  specialized  devices  are  known 
to  have  been  evolved  early  in  the  history  of  fishes, — 
the  more  early  if,  as  Garman  has  supposed,  the  gill  fila- 
ments in  primitive  sharks  protruded  at  the  sides  of  the 
head.f  There  are  thus  the  gill-encasing  derm  frills  of 
the  archaic  sharks,  Cladoselache,  Chlamydoselache,  and 
Acanthodes  (pp.  78-83),  or  of  Chimaeroids  (p.  100).  These 
protective  structures,  the  writer  believes,  may  well  have 
originated  independently  even  within  the  limits  of  sub- 
groups. They  have  certainly  no  direct  relation  to  the 
opercle  of  bony  fishes. 

Modes  of  respiration  by-gill  filaments  have  been  found 
in  endless  variety  among  fishes,  clearly  dependent  in  the 
majority  of  cases  upon  environment.  Thus  fishes  that 
require  a  temporary  existence  out  of  water  will  be  found 
to  have  specialized  spongy  gill  filaments  and  a  closely  fit- 
ting gill  cover  to  keep  moistened  the  respiratory  organs 
(e.g.  Callichthys,  p.  172). 

*  Thus  in  many  bony  fishes,  e.g.  mullet  or  Brevoortia  (menhaden),  the 
inner  margins  of  the  gill  bars  are  fringed  with  what  appears  like  the  finest 
gauze,  each  gill  raker  giving  off  primary,  secondary,  and  tertiary  branches.  A 
somewhat  similar  condition  occurs  in  the  shark,  Selache  (p.  90). 

t  This  condition  appears  to  have  been  possessed  by  the  Lower  Carbo- 
niferous Cladoselache. 


S  WIM-BLADDER  2 1 

To  live  a  longer  time  out  of  water  has  been  rendered 
possible  only  by  the  appearance  of  a  lung-lil^e  organ.  Such 
a  structure,  however,  would  have  been  of  too  great  impor- 
tance in  the  living  economy  of  terrestrial  vertebrates  to 
have  had  a  sudden  origin  :  it  may  most  reasonably  have 
been  derived  from  a  similar  structure  occurring  very  gener- 
ally among  fishes.  The  lungs  certainly  resemble  the  swim- 
bladder  of  fishes  in  so  many  important  characters  that  it 
seems  difficult  to  regard  these  organs  as  morphologically 
distinct.  In  itself  the  swim-bladder  must  be  looked  upon  x 
as  an  ancient  and  essentially  a  generalized  structure,  for 
within  the  groups  of  fishes  it  has  already  acquired  a  vari- 
ety of  modified  characters  :  appearing  in  a  lowly  condition 
in  sharks,  it  acquires  a  balancing  function  in  the  majority 
of  bony  fishes ;  in  some  forms  (carp,  siluroids)  its  function 
connects  it  with  the  auditory  organ,  often  by  a  highly 
elaborated  apparatus :  while  in  other  forms  (Amia,  Gar- 
pike,  Dipnoans),  it  is  unquestionably  of  respiratory  value. 
The  wide  range  in  the  characters  of  the  air-bladder  (cf. 
Figs.  13-19,  and  Table,  p.  264),  even  among  recent  fishes, 
would  naturally  favour  its  homology  with  the  lungs  :  it  may 
thus  be  paired  or  unpaired,  attached  by  its  duct  to  either 
the  dorsal,  lateral,  or  ventral  wall  of  the  gullet :  it  may 
present  the  most  varied  characters  in  its  lining  membrane 
or  in  its  vascular  supply.  When,  moreover,  it  becomes  of 
respiratory  value  (e.g.  Dipnoans,  Polyptenis),  the  gills  are 
known  to  become  in  part  degenerate.  The  larval  history 
of  amphibians,  presenting  so  perfect  a  transition  between 
gill-breathing  and  terrestrial  vertebrates,  should  alone  seem 
to  render  more  than  probable  the  general  homology  of  air- 
bladder  and  lung  —  an  homology  which  a  closer  knowledge 
of  the  conditions  of  the  lungs  of  the  lower  urodeles  (e.g. 
Nectitrus  may  well  be  expected  to  establish  definitely. 


LEP.DOSTEUS 
AND        AMIA 


ERYTHRINUS 


CERATODUS 


POLYPTERUS 

AND 

CALAMOICHTHYS 


LEPIDOSIREN 

AND 
PROTOPTERUS 


REPTILES 
BIRDS 

MAMMALS 


Figs.  13-19.  —  Air-bladder  of  fishes,  shown  from  the  front  and  sides.  Cf.  p. 
264.  A.  Air-  or  swim-bladder.  AD.  Air  duct.  D.  Digestive  tube.  (After  WILDER.) 
13.  Sturgeon  and  many  Teleosts.  14.  Amia  and  Lepidosteus.  15.  Erythrinus,  a 
Cyprinoid  Teleost.  16.  Ceratodus.  17.  Polypterus  and  Calamoichthys.  18.  Lepi- 
dosiren  and  Protopterus.  19.  Reptiles,  birds,  and  mammals.  The  diagrams  illus- 
trate the  paired  or  unpaired  character  of  the  organ,  its  varied  mode  of  attachment 
to  the  digestive  tube,  and  the  smooth  or  convoluted  condition  of  its  lining  mem- 
brane. 

22. 


SCALES  AND    TEETH  23 

The  mode  of  origin  of  the  lungs  as  an  unpaired  divertic- 
ulum  of  the  gullet  is  in  every  sense  similar  to  that  of  the 
air-bladder. 

2.   THE  DERMAL   DEFENCES   OF  FISHES 

The  dermal  defences  of  fishes  include  scales,  spines,  fin 
rays,  armour  plates,  and  teeth,  presenting  in  all  a  wide 
range  of  calcified  structures.  They  have  usually  an  outer, 
or  surface  layer  of  hard  enamel-like  texture  and  an  inner 
substance  heavy,  stout,  and  bone-like.  The  former  is  de- 
rived from  the  outer  layer  of  the  skin  (epidermis),  the 
latter  from  the  derma.  The  relation  of  these  structural 
parts  may  be  well  seen  in  a  section  of  shark  skin  which 
passes  through  one  of  its  minute  limy  cusps,  or  dermal 
denticles  (Fig.  20).  The  outer  skin  layer,  E',  originally 
covered  the  denticle,  which  grew  outward,  papilla-like, 
beneath  it ;  its  inner  surface,  in  contact  with  the  outgrow- 
ing papilla,  secreted  the  enamel,  E,  and  is  known  as  the 
enamel  organ,  EO:  at  the  cusp,  however,  the  epidermis  is 
early  worn  away.  The  bone-like  substance  of  the  tooth  is 
clearly  formed  in  the  lower  (dermal)  layer  of  the  skin,  D' : 
it  is  formed  by  the  calcification  of  the  outer  layers  of  the 
tip  and  base  of  the  dermal  papilla,  leaving  a  vascular  cavity, 
PC,  within.  This  limy  substance,  "  dentine,"  D,  presents 
microscopically  a  columnar  "  cancellated "  structure;  in 
this  and  in  its  lack  of  bone  cells  it  differs  structurally 
from  true  (cartilage)  bone. 

The  dermal  denticle  of  the  shark  is  certainly  the  sim- 
plest form  of  a  calcified  skin  defence  :  it  appears  to  repre- 
sent the  ancestral  condition  of  the  various  scales,  teeth, 
or  bone  plates  which  have  been  evolved  in  the  groups  of 
fishes.  It  is  usually  of  minute  size,  and  studs  closely  the 
entire  surface  of  the  skin,  forming  shagreen.  In  many 


27 


Figs.  20-31.  —  Mode   of  evolu- 
tion of  (teeth  and)  dermal  defences. 

20.  Shagreen  denticle  of  shark,  X  30, 
cross  section.    (After  HOFER.)     D. 
Dentine.     D'.  Derma.    E.  Enamel. 
£'.  Epidermis.  EO.  Enamel  organ. 
PC.  Pulp  cavity,  showing  nutritive 
tubules   passing   into   the    dentine. 

21.  Shagreen     denticle     ("  placoid 
scale  ")  of  Greenland  shark,  Lcemar- 
gus,  viewed  from  the  side  and  (A} 
top,  enlarged.     22.  Shagreen  denti- 
cles   of    shark,  Scyllium,    showing 
mode   of   arrangement,    x  30.    23. 
Shagreen  of  sting-ray,    Urogymnus, 
nat.  size.      (After  SMITH  WOOD- 
WARD.)    24.  Ganoid  dermal  plates  of  Lepidosteus.    A.  Inner  face  of  ganoid  plates, 
showing  tile-like  device  of  interlocking.     25.  Variation  of  ganoid  plates  in  Aetheolepis. 
(After  SMITH  WOODWARD.)     Plates  from  different  regions  vary  in  outline  from  cir- 
cular to  lozenge  shape.      26.  Coalesced   ganoid   plates   of  the   siluroid   Calhchlhys. 
27.  Jaw  of  Port  Jackson  shark,  Cestracion.     28.  Dental  plate  of  extinct  cestraciont  (?), 
Sandalodus.    29.  Dental  plates  of  jaw  of  sting-ray,    Trygon   (?).     30.  Dental  plates 
of  eagle-ray,  Myliobatis.    31.  Scales  of  Teleost.    A.  A  single  scale  enlarged. 

24 


EVOLUTION   OF  SCALES  2$ 

members  of  the  shark  group  the  denticles  are  scattered 
over  the  body  without  traces  of  metameral  arrangement 
(Fig.  23) ;  in  others  they  acquire  a  segmental  position 
(Fig.  22).  Usually  the  denticles  possess  very  definite 
shapes  and  regional  characters ;  their  basal  portion,  where 
implanted  in  the  skin,  may  thus  become  of  enlarged  size 
and  regular  outline  (Fig.  21  A\  their  projecting  cusps 
tapering,  blunted  (Fig.  23),  or  branched.  Sometimes  the 
fusion  of  contiguous  denticles  may  occur  (as  in  the  en- 
larged blunted  denticles  of  Fig.  23). 

The  evolution  of  the  more  perfect  body  armouring  of 
fishes  from  shagreen  denticles  has  not  been  followed  in 
minor  details.  It  appears,  however,  that  the  calcifica- 
tion of  the  skin  which  occurs  superficially  in  the  dermal 
papillae  of  the  shark  may  in  other  fishes  be  traced  oc- 
curring in  deeper  and  deeper  layers  of  the  derma :  the 
papillae  at  the  surface  accordingly  lose  their  functional 
importance,  and  tend  to  disappear,  while  the  calcified 
tissue  of  the  derma  —  representing  morphologically  the 
basal  region  of  the  denticles  —  is  coming  to  occupy  more 
and  more  definite  tracts.  These  processes  have  already 
taken  their  origin  within  the  group  of  sharks. 

An  interesting  condition  in  the  subsequent  evolution  of 
the  dermal  armouring  is  illustrated  in  Fig.  25,  and  has 
been  described  by  Smith  Woodward.  The  circular  bone 
plate  of  the  figure  is  a  calcified  dermal  tract  which  still 
retains,  scattered  generally  over  its  surface,  traces  of 
shagreen  tubercles  :  from  this  shark-like  condition  a 
well-marked  gradation  in  the  form  of  the  derm  plates 
may  be  traced  in  different  body  regions  of  the  same 
fish :  according  to  metameral  needs  there  are  acquired 
rectangular  or  lozenge-shaped  outlines.  In  Fig.  24  these 
bone  or  "  ganoid "  plates  are  seen  to  constitute  a  com- 


26  EVOLUTION  OF  SCALES 

plete  but  flexible  body  armouring,  made  additionally 
strong  by  an  interlocking  articulation  of  its  elements 
(24  A). 

In  this  form  the  enamel-like  surface  layer  ("ganoine") 
of  the  ganoid  plates  is  believed  to  be  derived  from  the 
dentine  substance,  and  not  deposited  by  the  epidermis  : 
they  bear  numerous  shagreen  denticles  during  an  early 
period  of  life. 

The  most  complete  encasement  of  a  fish's  body  by 
dermal  plates  is  shown  in  Fig.  26,  v.  p.  172.  The  met- 
ameral  conditions  have  here  permitted  extended  fusions, 
a  single  dermal  plate  enclosing  the  upper,  or  lower 
division  of  the  muscle-plate  of  either  side. 

The  thin  horn-like  scales  of  the  majority  of  recent 
fishes,  e.g.  carp  or  perch  (Fig.  31  A)  are  probably 
derived  from  a  condition  not  widely  different  from  that 
of  Fig.  24.  They  take  their  origin,  however,  in  a  deeper 
layer  of  the  derma,  thence  grow  outward,  arising  as 
if  from  deep  and  flattened  pockets.  Their  substance 
becomes  horn-like,  rather  than  limy,  and  they  enlarge  in 
outline,  rather  than  in  thickness.  Their  hinder  margins, 
often  crenulate,  overlap  widely  the  neighbouring  scales ; 
their  arrangement  is  in  direct  relation  to  the  underlying 
metameres,  and  their  surface  is  densely  slime-coated. 
The  dermal  armouring  they  thus  constitute  is  both  light, 
tough,  and  flexible. 

Degeneration  of  scales  is  shown  to  occur  in  many 
types.  In  some  forms  their  size  may  become  micro- 
scopic (eel),  in  others  enormously  enlarged  (mirror  carp). 
In  cases  they  may  entirely  disappear  (leather  carp). 
The  fusions  of  the  dermal  plates  of  the  trunk-fish  or 
of  the  sea-horse  (p.  177)  are  probably  degenerate. 


TEETH  27 

Teeth 

Teeth  have  long  been  known  to  represent  the  dermal 
defences  of  the  mouth  rim.  In  this  region  they  have 
become  of  especial  value  in  the  living  economy  of  verte- 
brates—  seizing,  holding,  cutting,  or  crushing  the  food- 
material.  They  have  here  accordingly  been  retained  and 
specialized.  In  the  sharks  the  dermal  denticles  of  the 
mouth  rim  are  often  identical  in  shape  and  pattern  with 
those  of  the  entire  body  surface :  they  differ  only  in 
their  larger  size.  Their  arrangement  in  many  rows  still 
presents  clearly  their  metameral  character. 

The  forms  of  teeth  acquired  among  the  different  groups 
of  fishes  suggest  closely  the  evolution  of  the  more  modi- 
fied dermal  defences.  In  general,  they  are  found  to  vary 
widely  according  to  their  function  or  location  ;  those  near- 
est the  dermal  margin  of  the  mouth  usually  retaining 
the  cusp-like  and  more  primitive  features.  Thus  in  the 
jaw  of  Port  Jackson  shark  (Fig.  27,  v.  p.  85),  the  teeth  of 
the  symphysial  region  clearly  represent  shagreen  denti- 
cles ;  while  those  deeper  in  the  mouth,  large  and  blunt, 
serve  as  crushing  or  "pavement  "  teeth.  These  must  evi- 
dently be  looked  upon  as  standing  in  the  same  relation  to 
the  anterior  cusps,  as  do  the  bone  plates  of  Fig.  25  to  the 
derm  denticles  of  Fig.  23  ;  the  fused  crushing  teeth  have 
still  retained  their  metameral  arrangement.  The  dental 
plates  (Fig.  30)  of  a  ray,  Myliobatis  (p.  96)  show  more 
perfect  conditions  for  crushing ;  they  are  uniform  in  size, 
tightly  set,  and  present  a  smooth,  mosaic-like  surface.  A 
still  more  perfect  fusion  of  the  dental  elements  occurs  in 
a  ray,  closely  akin  to  Myliobatis  ;  all  lateral  elements  have 
here  been  fused,  but  their  metameral  sequence  has  been  re- 
tained (Fig.  29).  In  Fig.  28  is  shown  a  dental  plate  of  a 


23  TEETH  AND   SPINES 

fossil  shark  (?),  Sandalodus,  which  probably  represents  a 
condition  of  complete  fusion  ;  it  would  accordingly  cor- 
respond to  the  sum  of  the  dental  elements  of  half  of  the 
jaw  of  Fig.  27. 

In  more  highly  modified  fishes  the  tooth-producing 
region  has  become  greatly  extended  ;  teeth  are  present  not 
only  on  the  jaw  rims,  but  deep  in  the  mouth  cavity, 
studding  its  floor  and  roof,  and  occurring  even  on  the 
tongue,  gill  bars,  and  pharynx. 

Fin  Spines 

Primitive  dermal  defences  appear  to  have  played  a 
prominent  part  in  the  formation  of  fin  spines.  The  clus- 
tering of  dermal  cusps  on  the  exposed  margin  of  a  fin 
may  have  been  an  important  initial  step  toward  the  for- 
mation of  a  rigid  cutwater.  The  anterior  margin  of  the 
fin  of  Fig.  49  is  whitened  with  a  fusion  of  dermal  tuber- 
cles which  must  have  formed  a  firm  encrusting  support ; 
the  extension  of  the  calcification  of  the  bases  of  the  tu- 
bercles would  accordingly  be  the  mode  of  origin  of  a  fin 
spine.  In  Fig.  32  is  shown  a  spine  that  appears  largely 
of  this  origin.  A  similar  spine  (Fig.  33)  shows  its  dermal 
tubercles  not  only  at  its  sides,  but  in  a  most  marked 
way  at  its  hinder  margins.  In  Fig.  34,  representing  the 
"  sting  "  of  the  sting  ray,  a  series  of  dermal  spines,  bear- 
ing rows  of  minute  denticles  are  seen  to  arise  in  a  meta- 
meral  succession.  A  condition  somewhat  similar  is  known 
in  the  Carboniferous  shark,  Edestus  (Fig.  35),  whose  spine, 
often  of  gigantic  size,  is  of  special  interest,  since  it  shows 
how  important  a  part  in  spine-formation  may  be  taken  by 
the  dermal  defences  of  many  successive  metameres.  The 
spine  is  clearly  segmented,  and  as  its  separate  elements 
(Fig.  37)  are  bilaterally  symmetrical  (Figs.  36  and  38),  its 


FIN  SPINES 


position  was   probably  in   the   median  line  of   the  body. 
The  well-marked,  backward  curve  of   the  spine  suggests 


34 


Figs.  32-38.  —  Fin  spines.  32.  Fin  spine  and  pectoral  fin  of  Acanthodian. 
33.  Hybodus  (cestraciont  shark).  34.  Sting-ray,  Trygon.  35.  Edestus  heinrichsii 
(Carboniferous  shark,  known  only  from  its  spine),  side  view  of  spine.  X  \.  36, 
37,  38.  Dorsal  view,  separated  element  and  transverse  section  of  Edestus  spine. 

that  fin  structures  could  not  well  have  existed  behind  it. 
Each    separate  element  has  an  elongated   basal   portion, 


go  EVOLUTION  OF  FINS 

which  apparently  was  imbedded  in  the  integument ;  its 
gouge-like  form  (Figs.  37  and  38)  permitted  it  to  be  firmly 
apposed  to  its  anterior  and  posterior  neighbours.  Each 
median  enamelled  cusp  represents  apparently  the  sum  of 
the  shagreen  papillae,  occurring  in  the  median-dorsal  region 
of  each  metamere,  its  gouge-like  underlying  portion  the 
metameral  calcification  of  the  bases  of  the  denticles. 

What  has  been  the  mode  of  origin  of  the  primitive 
derm  cusps  is  a  puzzling  question.  It  is  significant,  per- 
haps, that  they  occur  in  primitive  forms  (sharks)  in  con- 
nection with  the  sense  organs  of  the  lateral  line  (p.  50), 
and  that  they  are  in  this  region  retained  in  a  number 
of  archaic  forms  (Polypterus,  p.  148,  Callichthys,  p.  172), 
which  have  in  all  other  body  parts  evolved  protective  derm 
plates.*  It  is  certain  that  for  the  sensory  groove  of  the 
lateral  line,  no  more  simple,  protective  devices  could  have 
arisen  than  conical  elevations  of  skin.  Arising  in  this 
region,  they  may  have  extended  their  protective  functions 
over  the  entire  body  surface. 

3.   THE  EVOLUTION  OF  FINS 

Fins  are  the  organs  of  progression  adapted  to  the 
needs  of  aquatic  living.  A  fish,  balanced  in  its  living 
medium,  acquires,  as  has  been  seen,  a  boat-like  form, 
enabling  it  to  pierce  the  water  in  the  least  resisting 
\manner.  1  Its  appendages,  when  they  come  to  arise,  must 
reasonably  be  looked  to  to  fulfil  the  mechanical  condi- 
tions of  aquatic  motion  in  order  to  propel  to  the  best 
advantage  the  lightly  balanced  and  boat-shaped  mass. 
Fins  might  thus  be  expected  to  arise  as  keel-like  struct- 

*  In  the  sensory  canals  of  the  head  of  Chimsera,  the  presence  of  scattered 
bony  plates,  protective  in  function,  v.  p.  1 14,  would  suggest  the  concentration 
of  the  marginal  cusp  elements  for  more  perfect  protection. 


MEDIAN  FINS  31 

ures,  i.e.  as  ridges  in  the  direction  of   the  fish's  axis  or 
line  of  motion. 

Fish  fins  have  long  been  distinguished  as  vertical  (me- 
dian, or  unpaired)  or  lateral  (paired),  the  former  function- 
ing both  as  keel  and  means  of  propulsion,  the  latter  as 
accessory  and  specialized  balancing  organs.^ 

Median  Fins 

Median  fins  are  unquestionably  the  older.  They  exist 
in  the  simplest  condition  in  those  fishes  whose  axis  is  long 
and  whose  motion  is  undulating.  Indeed,  the  sole  swim- 
ming requisite  is  here  the  continuous  dermal  keel  which 
passes  down  the  back  from  the  head  to  the  body  terminal, 
and  extends  thence  forward  on  the  ventral  side.  The 
undulatory  motion  of  the  body  is  well  transmitted  to  the 
surrounding  medium  by  the  exaggerated  undulation  of 
this  long,  waving  fin  web.  This  condition  was  probably 
the  ancestral  one  in  the  evolution  of  fishes.  It  represents 
the  simplest  metamerism  ;  it  occurs  as  the  adult  condition 
in  the  lampreys  (p.  57),  and  as  the  embryonic  or  larval 
stage  in  all  fishes,  appearing  before  any  traces  of  paired 
fins  are  known  ;  .it  is  even  adverse  to  their  specialization  : 
should  life  habits  require  undulatory  motion,  paired  fins 
must  inevitably  tend  to  disappear  (eel,  p.  173  ;  Cala- 
moichthys,  p.  150). 

From  this  condition  the  further  evolution  of  the  un- 
paired fins  may  thus  be  theoretically  outlined. 

The  primitive  continuous  dermal  fin  could  have  been 
of  little  value  in  active  movement  :  its  more  rapid  undu- 
lations could  not  have  greatly  increased  the  rate  of  motion, 
since  its  web,  lacking  in  supports,  would  not  have  retained 
its  rigidity.  As  the  simplest  means  of  strengthening  the 
fin  fold,  "  actinotrichia  "  (Ryder),  appear  to  have  been  early 


32  EVOLUTION  OF  FINS 

evolved  (Fig.  39,  T) ;  these  are  slender,  unjointed  fin  sup- 
ports, passing  from  the  body  wall  to  the  margin  of  the 
fin,  appearing  to  arise  without  relation 
to  the  underlying  body  segments.  The 
more  rapid  undulations  of  the  contin- 
uous fin  would  next  cause  nodes  to 
arise ;  and  at  other  points  the  greatest 
mechanical  stress  would  occur.  These 
portions  of  the  fin  web  would  accord- 
ingly become  prominent,  while  the  in- 
tervening or  useless  parts  would  dimin- 
ish in  width  and  tend  to  disappear.  The 
body  terminal  (tail,  caudal  fin)  has  now 
*  become  the  seat  of  propulsion :  dorsal 
and  ventral  fins  arise  as  lobate  elements 
of  the  fin  fold,  functioning  as  vertical 
keels  in  the  region  of  the  body  where 
mechanical  stress  demands  them  (v.  Fig. 
40),  increasing  in  size  as  the  intervening 
portions  of  the  web  gradually  disappear. 
Their  rate  of  growth  is  doubtless  af- 
fected by  the  appearance  of  the  paired 
fins ;  for  even  at  an  early  period  of  de- 
velopment these  are  known  to  have  an 
important  function  in  balancing  the  fish. 
The  lappet-shaped  fins  (Fig.  40)  next 
acquire  more  rigid  supports.  Cartilagi- 
nous rod-like  elements  arise  within  the 
fin  web,  arranged  in  metameral  sequence, 
representing,  perhaps,  fusions  of  actino- 
trichia.  As  shown  in  Fig.  40,  these  car- 
Fig-  39-  —  Hypothet-  tilaginous  "radials"  R,  appear  to  be 

ical  ancestral  shark.  Let- 
ters as  on  p.  33.  largest  and  stoutest  in  the  widest  por- 


MEDIAN  FINS 


33 


tions  of  the  fin  lobe,  and  thence  to  taper  in  size  toward 
the  nodal  points  of  the  web.  Each  radial  appears  shortly 
to  segment  off  a  proximal  joint,  or  "basal"  cartilage,  B,  to 
secure  a  more  perfect  attachment  with  the  wall  of  the  body. 
The  subsequent  evolution  of  the  fins  appears  to  have 
been  determined  by  two  modifications  of  growth,  —  the 
clustering  of  the  radial  and  basal  elements,  and  the 
encroachment  of  newly  formed  marginal  (distal)  rays 


FIQ.40 


43 


Figs.  40-43.  —  Evolution  of  unpaired  fins.  40.  Plan  of  reduction  of  vertical  fin 
web  into  its  dorsal,  anal,  and  caudal  elements.  41.  Arrangement  of  fin  supports 
in  primitive  fin  {Cladoselache) .  42.  Plan  of  archaic  unpaired  fin  in  (larval)  shark. 
43.  Unpaired  fin  of  fossil  Crossopterygian,  Holoptychius,  (After  SMITH  WOOD- 
WARD.) - 

A.  Anal  fin.  B.  Cartilaginous  basal  (fin  support).  C.  Caudal  fin.  D.  Dermal 
margin  of  fin.  D' .  Anterior  and  D".  Posterior  dorsal  fin.  K.  Cartilaginous  radial 
(fin  support).  T.  Actinotrichia. 


upon  the  functions  of  the  older  fin  supports.  Three 
stages  in  this  metamorphosis  will  be  seen  in  Figs.  41-43. 
The  first  illustrates  the  dorsal  fin  of  an  ancient  shark 
(Cladoselache,  p.  79),  and  will  at  once  be  seen  to  present 
most  primitive  conditions^:  It  closely  resembles  the  theo- 


34  ANAL   AND  DORSAL  FINS 

retical  dorsal  fin,  D'  or  Z>"  of  Fig.  40.  The  form  of  the 
fin  suggests  the  lobate  constriction  of  the  continuous  fin 
web ;  its  radial  supports,  R,  extend  from  the  body  wall  to 
the  margin  of  the  fin,  and  between  them  traces  of  actino- 
trichia  are  to  be  seen.  The  anterior  margin  of  the  fin 
must  now  function  as  a  strong  cutwater,  its  supporting 
elements,  both  radial  and  basal,  tightly  clustering.  A  fin 
of  this  character  could  evidently  have  possessed  a  greater 
freedom  of  lateral  movement  in  its  hinder  than  in  its  an- 
terior part ;  and  thus  the  clustering  of  the  fin  supports 
becomes  of  especial  significance.  The  region  of  move- 
ment, restricting  itself  to  the  hinder  part  of  the  fin, 
permits  extensive  fusions  of  the  supporting  cartilages 
anteriorly,  and  leads  ultimately  to  exceedingly  complex 
conditions.  The  dorsal  fin  of  a  Coal  Measures  fish  (Ho- 
loptychius,  p.  15.1)  has  thus  (Fig.  43)  specialized  the  power 
of  lateral  movement  in  the  highest  degree.  The  length 
of  the  fin  has,  in  the  first  place,  become  greatly  compressed, 
a  process  which  seems  to  have  resulted  in  implanting  the 
anterior  basals,  B,  deeply  into  the  integument  and  in 
fusing  them  :  the  posterior  basals  then  appear  to  have 
been  everted  from  the  surface  of  the  body.  Here  they 
still  retain  their  segmental  arrangement,  but  are  irregular 
in  shape  and  reduce  in  size  distally. 

An  important  part  is  taken  by  the  dermal  margin  of 
the  fin  in  modifying  the  size  of  the  older  fin  supports. 
The  simplest  form  of  a  dorsal  fin  of  a  recent  shark  (Fig. 
42)  has  thus  more  than  half  of  its  functional  area  of  a 
dermal  origin,  although  in  other  regards  it  resembles 
closely  the  conditions  of  Fig.  41.  The  dermal  margin  of 
the  fin  has  apparently  increased  to  the  detriment  and 
consequent  reduction  of  the  cartilaginous  elements ;  -it 
produces  in  its  secondary  structures  light  flexible  horn- 


CAUDAL  FIN  35 

like  rays,  which  prove  stronger  and  more  serviceable  than 
the  heavier  radials ;.  it  seems  more  capable  of  adapting 
the  fin  for  special  uses. 

Accordingly,  in  many  forms  of  recent  fishes,  notably 
bony  fishes,  the  entire  fin  is  found  to  become  of  dermal 
origin  ;.  The  radio-basals,  greatly  reduced  in  number  and 
size,  extend  no  further  outward  than  the  base  of  the  fin ; 
they  are  usually  small  and  irregular,  and  are  often  deeply 
sunken  within  the  body  wall. 

After  this  glimpse  at  the  mode  of  origin  of  the  vertical 
fins,  i.e.  dorsals  and  anals,  the  history  of  the  final  vertical 

fin,  the  tail,  and  of  the  paired  fins  may  next  be  reviewed. 

f 
The  Caudal  Fin 

The  tail,  or  caudal  fin,  is  the  main  organ  of  aquatic 
propulsion,  and  it  is  doubtless  on  this  account  that  it 
presents  so  wide  a  range  in  its  structure  and  outward 
form.  From  the  earliest  times  there  are  found  fishes  of 
all  groups  whose  tail  shapes  are  tapering  (diphycercal,  Fig. 
47),  unsymmetrical  (Jieterocercal,  Figs.  45,  46),  or  squarely 
truncate  (homocercal,  Fig.  48),  as  the  mechanical  needs 
in  swimming  may  have  demanded. 

The  following  summary  of  the  mode  of  evolution  of 
the  caudal  fin  seems  to  be  warranted  by  study  of  fossil 
and  embryonic  forms.  The  vertical  fin  fold  of  the  ances- 
tral fish  was  probably  carried  around  the  body  terminal 
and  strengthened  by  constant  actinotrichia  (Fig.  39  C),  a 
condition  similar  to  that  (Fig.  44)  of  an  early  larval 
stage  of  living  fishes  (protocercy).  This  caudal  structure, 
however,  could  have  proven  Ba  value  only  in  sluggish 
undulatory  motion.  The  functional  needs,  which  gave 
rise  to  radials  anteriorly,  have  in  the  tail  region  produced 
firmer  and  stouter  fin  supports.  These  appear  both  on  the 


2 6  CAUDAL  FIN 

dorsal  and  ventral  sides,  but,  unlike  the  radials  of  the  anal 
or  dorsal  fins,  do  not  segment  off  basal  elements.  They 
first  occur  in  the  region  of  the  base  of  the  caudal,  as  in 
the  embryonic  stage  (Fig.  44,  R),  since,  perhaps,  it  is  in  this 
region  that  the  greatest  stress  occurs  in  propulsion.  It 
is  not  until  a  later  stage  that  their  metameral  sequence 
is  extended  backward  to  the  tip  of  the  vertebral  axis 
(Fig.  40,  Q. 

With  the  origin  of  cartilaginous  supports  there  seems 
to  have  arisen  a  mechanical  need  for  enlarging  the  ventral 
lobe  of  the  caudal;  -ft  is  here  certainly  that  in  the  majority 
of  early  forms  the  radials  appear  longer  and  stouter,  giv- 
ing rise  to  the  condition  of  heterocercy  of  Figs.  45  and  46. 
The  greater  functional  importance  of  the  radials  of  the 
ventral  region,  R+H,  is  acquired  contemporaneously  with 
the  upturning  of  the  end  of  the  vertebral  axis.  In  the 
tail  of  a  Lower  Carboniferous  shark  (Fig.  46,  v.  p.  79),  an 
extreme  degree  of  heterocercy  has  been  acquired  before 
the  radials  of  the  lower  lobe  have  extended  themselves  in 
the  hindmost  region  of  the  vertebral  axis  ;,the  ventral  web 
of  the  upper  tail  lobe,  accordingly,  is  still  strengthened 
by  minute  (dermal)  rays,  which  the  writer  believes  homol- 
ogous with  actinotrichia ; ,  6n  the  fin's  dorsal  side  the 
radials  have  been  abruptly  upturned  with  the  notochord, 
and  are  fused  into  a  compact  cutwater. 

The  plan  of  structure  of  the  shark's  caudal  fin  (Fig.  45) 
may  in  its  most  primitive  form  prove  to  be  the  ancestral 
one  of  fishes ;  if  this  is  the  case  it  would  give  rise  to  the 
types  of  caudal  fins  of  Figs.  47  and  48.  That  it  has  given 
rise  to  the  latter  form  cannot  be  doubted,  for  even  in  the 
adult  condition  of  the  fin  the  notochord,  N>  may  be  seen 
passing  to  the  upper  lobe  of  the  tail ;  the  essential  out- 
ward form  of  this  truncated,  or  homocercal,  tail  had  already 


Figs.  44-48.  —  Evolution  of  caudal  fin.  44.  Embryonic  caudal  of  Amia.  45.  Hetero- 
cercal  caudal  of  shark,  Cestracion.  46.  Heterocercal  caudal  of  Cladoselache.  47.  Diphy- 
cercal  caudal  of  Polypterus.  (After  L.  AGASSIZ.)  48.  Homocercal  caudal  of  Teleost. 
(After  RYDER.) 

D.  Dermal  fin  supports.  L.  Lateral  line.  M.  Spinal  cord.  MC.  Membranous  caudal. 
N.  Xotochord.  N+,  and  R+N.  Neural  spines,  including  probably  radial  and  basal 
elements.  R.  Radials.  R+H.  Haemal  arch  and  spine ;  includes  as  well,  probably,  radial 
and  basal  elements. 

37 


38  PRIMITIVE    CAUDAL  FIN 

been  acquired  in  ancient  sharks  (Fig.  46).     The  fin  of  Fig. 

47,  however,  has  not  generally  been  looked  upon  as  derived 
from  shark-like  conditions  ;/it  has,  on  the  other  hand,  been 
thought  to  be  most  nearly  of  the  ancestral  form.     The 
vertebral  axis  does  not  appear  to  be  upturned,  and  the 
ventral  and   dorsal  lobes   of  the  fin  remain  nearly  sym- 
metrical, or  diphycercal.     This  form  of  the  caudal  fin,  on 
the  other  hand,  has  been  noted  to  present  many  degener- 
ate characters,  arid  to  the  writer*  it  seems  more  reasona- 
ble to  regard  the  diphycercal  condition  as  in  many  cases 
directly  descended  from  the  heterocercal.      This  might  be 
effected  by  the  terminal  portion  of  the  vertebral  rod  abort- 
ing (as  in  Fig.  47,  N),  and  the  upper  and  lower  lobes  of  the 
tail  becoming  pressed  backward  until  their  hinder  margins 
appose  in  the  axial  line.f     The  form  of  diphycercy  which 
is  seen  in  Fig.  1 19  is  unquestionably  of  little  morphological 
value  ;,ft  occurs  commonly  in  deep-sea  fishes  of  every  group, 
and  must  be  looked  upon  as  a  degenerate  condition  result- 
ing from  impeded  motion  under  the  conditions  of  bathyb- 
ial,  or  deep-sea  living. 

The  cartilaginous  supports  of  the  caudal,  like  those  of 
other  unpaired  fins,  become  greatly  reduced  in  size  by  the 
encroachment  of  dermal  rays.  In  the  tail  of  the  fossil 
shark  (Fig.  46)  the  cartilaginous  supports,  R,  extend  to  the 
very  margin  of  the  fin  :.  an  the  modern  shark  (Fig.  45)  a 
large  part  of  the  functional  fin  area  has  become  of  second- 
ary, or  dermal  origin,  D,  In  the  caudals  of  Figs.  47  and 

48,  distinct  dermal  rays,  D,  are  seen,  extending  from  the 
body  wall  to  the  fin  margin,  splitting  and  segmenting  dis- 
tally  in  becoming  more  perfectly  specialized  in  function. 
The  cartilaginous  supports,  R  +  Nand  R  +  H,  must  now  be 

*  Journal  of  Morphology,  IX,  i,  1894. 
t  Gephyrocercy  of  Ryder. 


PAIRED  FINS  29 

looked  upon  as  including  the  elements  of  both  the  radials 
and  the  haemal  or  neural  processes  and  spines. 

The  Paired  Fins 

The  paired  fins  of  fishes  claim  an  especial  interest  as 
the  precursors  of  the  limbs  of  the  land-living  vertebrates. 
In  this  light  they  have  been  widely  studied,  and  many 
schemes  have  been  devised  for  the  comparison  of  the  parts 
of  the  five-fingered  extremity,  or  cheiropterygium,  of  the 
amphibian  with  the  fin  structures  of  many  fishes.  The  un- 
satisfactory character  of  these  homologies,  however,  is  felt 
at  the  present  time  more  generally  than  ever,  and  many 
morphologists  believe  with  Dr.  Mollier  *  that  the  ancestral 
form  of  the  terrestrial  limb  cannot  be  found  in  any  of  the 
known  types  of  paired  fins^^^^T**" 

Among  fishes,  on  the  other  hand,  there  appears  to  be  a 
well-marked  unity  of  plan  in  the  varied  forms  of  the 
paired  fins£  and  there  exists  so  perfect  a  gradation  in 
structural  characters  in  the  different  forms  that  it  seems 
impossible  to  doubt  their  genetic  kinship.  Which  fin, 
however,  must  be  looked  upon  as  the  ancestral  type  is  still 
disputed.  Professor  Gegenbaur  has  long  maintained  that 
the  fin  of  Fig.  54  (or,  better,  the  pectoral  fin  of  Fig.  147!) 
is  to  be  looked  upon  as  the  most  primitive  form,  or  Archip- 
terygium.  It  is  a  leaf-shaped  fin,  whose  principal  carti- 
laginous supports  are  arranged  in  a  row  from  base  to  tip 
in  the  position  of  a  mid-rib  tf  and  whose  minor  fin  supports 
are  grouped  more  or  less  symmetrically  on  either  side  of 
this  axis  (cf.  Figs.  53,  54,  121,  123,  126).  The  archipteryg- 
ium  is  believed  by  Gegenbaur  to  have  had  a  centrifugal 
origin  :  it  arose  behind  the  gill  region,  representing  in  its 

*  SB.  Gesell.f.  Morph.  Munchen,  1894,  p.  17. 

t  Gegenbaur,  Das  Flossenskelet  der  Crossopterygier.     Cf.  Morph.  JB,  1894. 


40  LATERAL  FOLD  FINS 

supporting  substance  the  fusion  of  the  cartilages  of  the 
hindmost  gill  bars.;  in  its  outward  growth  the  median  axis  of 
the  fin  was  first  produced,  the  minor  supports  then  arrang- 
ing themselves  on  both  anterior  and  posterior  margins. 
The  fin  of  Fig.  52  was  believed  to  represent  a  specially 
evolved  (or  "monoserial")  form  of  the  archipterygiumr.the 
hindmost  of  its  elements,  B,  was  homologized  with  the 
primitive  fin  stem,  along  whose  posterior  (post-axial)  mar- 
gin the  elements,  R,  no  longer  occurred.  The  structures 
of  Fig.  53  were  adduced  as  a  transitional  stage  in  the  dif- 
ferentiation of  the  biserial  archipterygium  (Fig.  54)  into  the 
monoserial  form  of  Fig.  52. 

The  theory  of  Gegenbaur  as  to  the  origin  and  evolution 
of  the  paired  fins  cannot  be  said  to  be  in  any  way  generally 
supported  at  the  present  time.  The  opposing  view,  that 
of  their  derivation  from  a  continuous  lateral  dermal  fin 
fold,  based  on  the  work  of  Thacher,  Balfour,  Mivart, 
Dohrn,  Wiedersheim,  and  others,  is  widely  accepted,  and 
continues  to  gain  supporting  evidence  on  the  sides  both 
of  embryology  and  palaeontology. 

In  the  following  discussion  of  the  paired  fins  the 
writer  has  mainly  followed  the  recent  studies  of  Wieders- 
heim.* 

The  paired  fins  are  believed  to  have  arisen  as  balancing 
organs,  accessory  in  function  to  the  vertical  fins.  They 
probably  occurred  early  in  the  line  of  descent  as  a  response 
to  a  need  for  balancing  the  fish's  body,  at  the  time  when 
the  vertical  fin  was  separated  into  caudal,  dorsal,  and  anal 
elements.  There  can  be  little  doubt  that  they  first  arose 
in  the  line  of  the  fish's  motion,  and  are  known  primitively 
(Figs.  49,  50),  as  a  pair  of  keel-like  lateral  lappets  arising 
somewhat  ventrally,  and  directed  outward  and  downward. 

*  Das  Gliedmassenskelet  der  Wirbdthiere,  1893. 


PAIRED  FINS  4I 

The  foremost  pair  appears  anteriorly  not  far  behind  the 
gill  region  :  from  its  position  it  has  certainly  the  more  im- 
portant mechanical  function  in  balancing  the  fish's  length 
—  on  this  account  becoming  more  widely  modified  in  form 
and  function  as  the  pectoral  fins.  The  hinder  pair,  or  ven- 
tral fins,  though  in  the  plane  of  the  pectorals,  has  a  more 
ventral  position,  the  hinder  borders  converging  in  the 
region  of  the  anus.  The  ventral  fins  are  certainly  placed 
in  the  most  motionless  region  of  the  fish:  they  are  little 
affected  by  either  the  lateral  or  upward  movements  of  the 
body ;  and  remain  accordingly  smaller  in  size  and  simpler 
in  structure  than  the  pectoral  fins.  That  there  may  have 
existed  in  primitive  fishes  a  third  (post-ventral)  pair  of  fins 
is  by  no  means  improbable  (cf.  T.  J.  Parker,  Ref.  p.  244), 
although  its  presence  has  not  as  yet  been  satisfactorily 
demonstrated. 

The  paired  fins  thus  appear  to  have  been  derived  from  a 
continuous  dermal  fold,  similar  in  every  way  to  that  giving 
rise  to  the  vertical  fins.  They  appear,  moreover,  to  have 
undergone  the  same  mode  of  evolution  in  their  structures' 
as  have  the  dorsal  or  anal  fins.  The  unpaired  fin  fold  as  it 
passed  forward  on  the  ventral  side  of  the  body  may  primi- 
tively have  forked  in  the  anal  region,  and  given  rise  on 
either  side  to  a  lateral  fold.  In  these  might  next  appear 
an  anterior  and  posterior  pair  of  lappets,  —  pectoral  and 
ventral  fins,  —  whose  positions  would  be  determined  by 
mechanical  needs,  and  whose  size  would  increase  as  the 
intervening  and  useless  portion  of  the  dermal  fold  disap- 
peared. In  the  subsequent  history  of  pectoral  and  ventral 
fins,  supporting  elements,  actinotrichia,  radials,  and  basals, 
would  arise  in  the  same  way  as  in  the  unpaired  fins,  and  a 
similar  metamorphosis  of  the  fin  form  would  take  place, 
owing  to  the  concrescence  of  these  elements  and  to  the 


FIG.  49 


Figs.  49-54.  —  Evolution  of  paired  fins.  49-50.  Pectoral  and  ventral  fins  of  Cladose- 
lache.  X  5.  51.  Pectoral  fin  of  Acanthodian,  Parexus.  (After  SMITH  WOODWARD.)  52. 
Pectoral  fin  of  Heptanchus.  (After  GEGENBAUR.)  53.  Pectoral  fin  of  Xenacanthus 
(Pleuracanthus.)  (After  A.  FRITSCH.)  54.  "  Archipterygial  "  pectoral  fin  of  Ceratodus. 
(After  HOWES.) 

B.  Basal.    D.  Dermal.    R.  Radial. 

42 


PAIRED  FINS      .  43 

subsequent  encroachment  of  the  dermal  fin  margin.  These 
conditions  may  be  briefly  illustrated.  The  paired  fins  of  a 
primitive  shark  (Figs.  49,  50,  v.  p.  79)  appear  as  the  actual 
lappet-shaped  remnants  of  a  continuous  dermal  fold.  The 
ventral  fins  (Fig.  50)  have  clearly  retained  even  the  out- 
ward shape  of  the  fin  fold ;  the  supporting  elements  are 
arranged  in  metameral  order  ;  the  radials,  R,  are  unjointed, 
extending  from  body  wall  to  fin  margin  ;  the  basals,  agree- 
ing in  number  with  the  radials,  are  uniform  in  size,  and  as 
yet  unfused.  The  pectorals,  acquiring  more  special  func- 
tions (Fig.  49),  are  enlarged  in  size,  their  basals,  B,  becom- 
ing compressed  and  obscure.  In  these  fins  the  effect  of 
concrescence  is  admirafry  marked ;  the  anterior  fin  margins, 
pressed  tail-ward  in  their  plane  of  growth,  become  firm  and 
rigid,  their  elements  stout  and  compact ;  the  basals,  re- 
sponding to  this  outward  need,  cluster  more  firmly  together, 
are  compressed  and  fused,  their  anterior  elements,  largest 
and  stoutest,  become  inturned,  their  posterior  elements, 
slightest  and  most  clearly  metameral.* 

The  next  stage  in  the  evolution  of  the  paired  fins  is 
clearly  comparable  to  that  already  noted  as  occurring  in 
the  dorsal  fin  of  Holoptychius  (Fig.  43),  where  the  line  of 
basals,  fusing  compactly  into  a  plate-like  mass,  had  in- 
turned  its  anterior,  andf  protruded  its  posterior  tip ;  a 
change  apparently  slight,  but  great  in  functional  impor- 
tance. Up  to  this  stage  the  fin  has  been  firmly  implanted 
in  the  body  wall ;  its  motion,  probably  slight  upward  or 
downward,  served  but  to  balance  the  fish,  its  fin  rays, 
tending  to  concentrate  anteriorly,  functioned  as  an  efficient 
cutwater.  This  process  of  concentration  in  the  anterior 
fin  margin  may  have  resulted,  the  writer  believes,  in  the 

*  The  effect  of  the  enlarged  and  clustering  dermal  denticles  in  strengthen- 
ing the  cutwater  margin  of  the  fin  has  already  been  noted  (p.  28). 


44  PAIRED   FINS 

formation  of  fin  spine,  as  in  Acanthodian  *  (Figs.  32,  51, 
and  p.  81).  But  the  protrusion  of  the  line  of  the  basals 
must  have  brought  with  it  a  new  use  in  the  economy  of 
fish  motion.  The  plane  of  the  fin  could  now  be  directed 
upward  or  downward ;  the  fin  would  become  a  direct  aid 
in  propulsion ;  it  would  acquire  a  paddle-like  function  ;  it 
could  also  be  extended  sideways  as  a  check  to  motion. 
Under  these  circumstances  it  is  not  unnatural  that  the 
region  of  the  concrescence  of  the  fin  rays  should  now  be 
transferred  from  the  fin's  anterior  to  the  more  useful  pos- 
terior (now  distal)  margin,  and  that  the  fin  rays,  as  well  as 
the  line  of  basals,  should  acquire  a  more  jointed  structure, 
suited  to  flexible  motions.  The  course  of  the  differentia- 
tion of  fin  structures  may  be  traced  from  this  point  on- 
ward, as  Wiedersheim  has  shown,  by  means  of  a  series  of 
gradational  stages :  from  the  conditions  of  Fig.  49  we  may 
in  the  present  figures  pass  to  those  of  Fig.  52,  thence  to 
those  of  Figs.  53  and  54.  In  the  pectoral  fin  of  a  modern 
shark  (Fig.  52)  the  basal  cartilages,  B,  may  still  be  com- 
pared with  those  in  the  older  form  (Fig.  49  B]  ;  their  distal 
element  (B,  at  the  right  of  the  figure),  however,  protrudes 
from  the  body  wall  and  is  becoming  surrounded  by  clus- 
tered radials,  R ;  the  cartilaginous  elements,  it  is  here 
noted,  have  been  placed  in  competition  with  the  dermal 
elements,  and  have  already  yielded  them  over  half  of  the 
fin  area.  In  the  next  stage  of  the  evolution,  as  in  the 
pectoral  fin  of  a  Permian  shark  (Pleuracanthus,  p.  83,  Fig. 
53),  the  line  of  the  basals  is  seen  to  boldly  protrude  from 
the  body  wall  and  to  have  become  distinctly  jointed ;  the 
radials  have  surrounded  its  distal  end,  and  taken  a  position 

*  This  homology  proposed  by  the  writer  has  not  been  accepted  by  Smith 
Woodward;  the  spine  is  unquestionably  encased  outwardly  by  dermal  den- 
ticles. 


PAIRED  FINS  45 

along  the  outer  half  of  the  hinder  margin  of  the  fin  stem  ; 
the  dermal  region  of  the  fin,  D,  has  notably  increased. 
Indeed,  the  fin  area  in  the  modern  bony  fishes  (Fig  145, 
PF)  may  become  entirely  dermal,  and  the  basal  supports 
greatly  reduced  and  metamorphosed.  In  a  final  type  of 
fin  (Fig.  54)  the  line  of  the  basals  has  become  widely  spe- 
cialized, and  the  characters  of  the  archipterygium  have 
been  attained  :  the  fin  stem  is  long,  tapering,  jointed ;  the 
radials  occur  as  clearly  along  the  hinder  as  along  the  ante- 
rior margin;  and,  as  in  Figs.  52,  53,  dermal  rays  contrib- 
ute largely  to  the  fin  area.  This  form  of  fin  may  be  noted 
as  most  closely  approximating  in  function  the  limb  type  of 
land-living  vertebrates. 

It  has  recently  been  urged  that  the  lateral  fold  origin  of 
the  paired  fins  as  thus  described  is  not  confirmed  by  devel- 
opmental studies, — the  especial  ground  for  this  belief 
being  that  in  sharks  these  fins  appear,  even  in  very  early 
stages,  as  paired  lappet-like  outgrowths,  destitute  of  inter- 
vening fin  membrane.  The  perfected  fin  fold  is  therefore 
claimed  to  represent  nothing  more  than  a  specialization  to 
bottom-living,  since  this  condition  is  known  to  maintain  in 
earlier  stages  and  in  more  primitive  metamerism  in  the 
development  of  skates  :  and  as  skates  (p.  93)  are  well  known 
to  represent  a  comparatively  recent  offshoot  from  the  stem 
of  the  sharks,  it  is  accordingly  inferred  that  the  chief  proof 
of  the  lateral  fold  doctrine  is  destroyed. 

Since  these  objections,  however,  were  raised,  the  struct- 
ural conditions  of  the  ancient  shark  of  Figs.  49  and  50 
have  been  described,  and  may  be  looked  upon  as  the 
weightiest  evidence  of  the  origin  of  paired  fins  from  lat- 
eral folds.  Nor  does  it  seem  to  the  present  writer  that 
the  early  character  of  the  fin-fold  metamerism  of  skates 
is  to  be  looked  upon  as  an  unexpected  condition.  Their 


46 


SENSE    OK  CANS   OF  FISHES 


broad  longitudinal  fins,  specialized  to  bottom-living,  become 
fashioned  in  an  ancestral  mould ;  and  it  seems  not  unnatu- 
ral that  they  tend  to  reacquire  their  latent  primitive  form 
at  an  early  period.  On  the  other  hand,  the  fin-fold  condi- 
tion of  the  shark  might  be  less  perfectly  shown  on  account 
of  processes  of  accelerated  development. 

4.    THE  CHARACTERS  OF  THE  SENSE  ORGANS  OF  FISHES 

It  has  already  been  seen  that  the  conditions  of  aquatic 
living  have  caused  fishes  to  evolve  adaptive  structural  char- 
acters, such  as  body  form,  specialized  metamerism,  organs 
of  progression,  and  dermal  investiture.  It  is  not,  accord- 
ingly, unnatural  to  expect  that,  from  the  same  causes,  the 
condition  of  the  sense  organs  may  have  been  strikingly 
modified. 

The  sense  of  "feeling"  —using  the  word  in  its  general 
meaning  —  has  been  of  especial  value  in  fishes,  and  tactile 
organs  appear  to  be  independently  developed  in  all  fish 
groups  whose  living  habits  demand  them.  In  the  form  of 
barbels  they  thus  occur  in  members  of  the  various  divis- 
ions of  bony  fishes,  as  cod  (cusk,  Ophidium)  (Fig.  55), 
drum-fish,  Pogonias  (Fig.  56),  or  sculpin,  Hemitripterus 
(Fig.  57).  Their  form  may  be  lobate,  thread-like,  or  villose  ; 
they  are  often  surprisingly  similar  in  size,  position,  and 
innervation ;  they  usually  appear  on  the  inferior  head 
surface,  most  often  in  the  anterior  throat  region,  in  the 
position  most  exposed  to  tactile  impressions.  The  thread- 
like barbels  of  the  catfishes  (Fig.  58,  p.  171)  are  arranged 
in  pairs  about  the  margin  of  the  mouth  ;  the  longest  lat- 
eral pair  is  connected  with  the  marginal  bone  (maxillary) 
of  the  upper  jaw  and  directed  at  will.  In  other  mud-living 
forms,  sturgeons  (Fig.  160),  the  barbels  have  arisen  on  the 
under  side  of  the  shovel-like  snout,  directly  in  advance  of 


Figs.  55-60.  —  Barbels  and  tactile  sense  organs.  (After  GOODE  in  U.  S.  F.  C.) 
55.  Cusk,  Ophidium.  56.  Drum-fish,  Pogonias.  57.  Sea-raven,  Hemitripterus. 
58.  Catfish,  Amiurus.  59.  Spoon-bill  sturgeon,  Polyodon  (ventral  view  of  snout). 
60.  Sea-robin  (Gurnard),  Prionotus. 

47 


48 


BARBELS  AND  LATERAL   LINE 


the  protractile  sucking  mouth.  There  can  be  little  doubt 
that  the  most  aberrant  tactile  organ  in  fishes  is  the  long 
spatulate  rostrum  of  the  paddle-fish  (Polyodon)  of  the  Mis- 
sissippi (Fig.  59)  :  the  sense  organs  are  here  known  to  be 
most  highly  specialized,  although  their  intimate  structure 
is  as  yet  not  understood.  Tactile  organs  are  often  to  be 
found  upon  fin  structures,  especially  those  of  the  anterior 
body  region.  In  the  sea-robin,  Prionotus  (Fig.  60),  the  sen- 
sory structures  are  borne  by  three  anterior  fin  rays  ;  these 
are  greatly  enlarged,  lose  their  connecting  fin  web,  and 
can  be  moved  at  will  in  a  variety  of  ways.  In  all  cases 
the  barbels  appear  to  be  true  and  highly  specialized 
organs  of  touch,  and  the  end  organs  are  comparable  ap- 
parently with  the  touch  papillae  of  higher  forms.  Of  their 
extreme  sensitivity  there  can  be  no  doubt,  and  as  far  as 
can  be  judged  from  their  innervation,  it  would  appear  that 
their  function  is  tactile  rather  than  gustatory,  as  has  been 
suggested.  The  limits  of  these  processes,  however,  are 
no  doubt  poorly  defined  in  aquatic  living. 

The  Lateral  Line 

The  sense  organs,  generally  known  as  the  lateral  line, 
or  mucous  canal  system,  are  looked  upon  as  essentially 
peculiar  to  fishes.  In  the  form  of  a  'lateral  line,'  they 
are  arranged  more  or  less  segmentally  along  the  median 
line  of  either  side  of  the  body  and  form  a  conspicuous 
feature  in  the  outward  appearance  of  the  fish  (Figs.  87, 
104,  LL,  121,  LL,  145,  LL).  Often  by  striking  colora- 
tion, the  lateral  line  is  rendered  even  more  prominent, 
passing  from  the  head  to  the  tail  as  a  pale  or  brightly 
coloured  band,  against  the  dusky  side  of  the  fish.  In  the 
region  of  the  head,  however,  this  sensory  structure  is,  as 
a  rule,  no  longer  conspicuous  :  it  dips  below  the  skin  sur- 


LATERAL  LINE    ORGANS  ^ 

face  and  becomes  a  series  of  interconnecting  tubes,  which 
pass  along  the  most  exposed  ridges  of  forehead,  cheek, 
orbit,  and  jaw  rim.  Here  in  different  regions,  these  sen- 
sory mucous  tubes  may  become  dilated,  constricted,  or 
ramose,  and  may  communicate  with  the  surface  by  occa- 
sional or  numerous  pores. 

The  mucous  canal  system  has  long  been  a  subject  of 
study  and  investigation.  It  is  looked  upon  generally  as  a 
sensory  organ,  adapted  to  the  conditions  of  aquatic  living, 
but  its  function  has  not  been  definitely  established.  How 
it  was  acquired,  or  how  its  ancestral  conditions  have  been 
modified  in  the  present  groups  of  fishes,  must  at  present 
be  looked  upon  as  in  many  ways  doubtful. 

The  simplest  conditions  of  the  mucous  canal  system 
appear  to  exist  in  primitive  sharks :  and  to  these  the 
writer  believes  that  the  modified  sense  canals  in  other 
fishes  may  best  be  referred. 

The  ancestral  condition  of  the  lateral  line  of  sharks 
appears  to  have  been  represented  in  an  open  continuous 
groove,*  lined  with  ciliated  sense  cells,  and  protected 
only  by  an  overcropping  margin  of  shagreen  denticles 
(Fig.  61).  In  this  condition  it  at  least  exists  in  the 
ancient  sharks  of  Figs.  86,  87,  92,  and  in  the  Chimaera 
(Fig.  104).  That  the  canals  of  the  head  region  were  also 
primitively  of  this  character  appears  exceedingly  prob- 
able :  they  are  thus  retained  in  the  adult  Chimaera  (Fig. 
104,  M.C)j 

In  the  modern   forms  of   sharks   the  condition  of  the 


*  It  is  to  be  noted  that  this  condition  occurs  in  deep-sea  fishes :  it  here  is 
evidently  an  adaptation  to  their  peculiar  environment,  which  causes  an  early 
ontogenetic  stage  to  be  permanently  retained. 

f  In  Callorhynchus  this  condition  has  been  largely  lost :  the  outer  margins 
of  the  sensory  groove  have  sealed  over. 
E 


FIG.  6.1 


68 


I'll 


N 


Figs.  61-68. —  Mucous  canals  (lateral-line  organs).  61.  Chlamydoselache, ,  groove-like 
lateral  line.  (After  CARMAN.)  62.  Plan  of  lateral  line  of  sharks,  longitudinal  section. 
63.  Plan  of  sensory  end  buds  (lateral  line).  64.  Sensory  tracts  of  head  of  larval  Amia. 
65.  Surface  openings  of  tubules  of  sensory  tracts  of  head  of  adult  Amia.  66.  Ramification 
of  sensory  tubules  in  dermal  plate  of  Amia.  67.  Cycloid  scales  of  Amia,  showing  the 
openings  of  the  tubules  of  the  lateral  line.  68.  Cycloid  scale  of  the  lateral  line  of  Amia, 
showing  the  course  of  the  sensory  tubule.  (Figs.  64-68  after  ALLIS.) 

N.  Nerve  supply.  S.  Sensory  tissue.  *  Denotes  an  outer  opening ;  -*  the  direction 
of  an  incoming  stimulus. 

50 


LATERAL  LINE    ORGANS  tjr 

sensory  canals  suggests  the  modifications  to  which  the 
open  sensory  groove  has  been  subjected.  There  are  thus 
forms  in  which  the  canal  becomes  more  and  more  deeply 
sunken  in  the  integument,  and  acquires  a  tubular  char- 
acter by  the  fusing  together  of  its  outer  margins.  The 
section  of  the  lateral  line  of  the  Greenland  shark,  Lce- 
margus  (Fig.  62,  v.  p.  90),  shows  the  tube-like  sensory 
canal  well  sunken  from  the  surface,  but  retaining  met- 
ameral  openings  at  the  points.  The  sensory  cells,  S, 
are  no  longer,  as  in  Fig.  61,  scattered  evenly  along  the 
floor  of  the  canal ;  they  now  occur  in  metameral  masses 
supplied  with  a  distinct  nerve  branch,  N,  located  in  the 
region  immediately  below  the  external  tubules.  When 
sunken  in  the  integument,  the  sensory  canal  is  known  to 
have  acquired  supporting  structures  to  enable  its  tubular 
character  to  be  maintained ;  in  the  Cretaceous  shark, 
Mesiteia,  an  elaborate  series  of  surrounding  calcified  rings  * 
were  thus  evolved. 

Further  changes  in  the  mucous  canal  are  often  accom- 
panied by  the  subdivision  of  the  external  apertures  ;  each 
of  the  openings  of  Fig.  62  might  by  this  process  give  rise 
to  a  series  of  minute  surface  pores,  as  at  vS  in  Fig.  65,  or 
enlarged,  showing  the  collecting  mucous  canals  in  Fig.  66. 
This  ramose  mode  of  termination  of  the  external  tubules 
has  been  admirably  described  by  Allis  f  in  the  ontogeny  of 
a  ganoid  ;  in  a  larval  stage  (Fig.  64,  S,  S,  S),  the  condi- 
tion of  the  sensory  canals  is  seen  to  differ  little  from 
those  shown  in  section  in  Fig.  62  ;  although  imbedded 
in  the  integument,  occasional  pores  are  seen,  S,  S,  to 
open  to  the  surface ;  these  subsequently  by  repeated  sub- 
division give  rise  to  the  great  number  of  minute  open- 

*  A  condition  somewhat  similar  has  been  noted  (Leydig)  in  Chimsera. 
t  On  the  Lateral  Line  System  of  Amia  calva.     J.  of  Morph.,  1889. 


C2  LATERAL  LINE 

ings  already  noted  in  Fig.  65.  A  process  of  this  kind 
is  carried  to  great  lengths  among  the  fishes  which 
develop  horn-like  scales,  as  Amia,  herring,  or  cod  :  in  the 
scales  of  the  lateral  line  region  the  distal  tubules  appear 
at  the  surface  as  a  cluster  of  pores,  as  shown  in  Fig.  67, 
or  in  the  detached  scale  of  Fig.  66. 

The  organs  of  the  lateral  line  (of  a  bony  fish)  shown 
in  section  in  Fig.  63  are  regarded  by  the  writer  as  of 
a  highly  modified  character.  They  appear  to  have  been 
derived  from  the  conditions  of  Fig.  62  ;  the  end  organ, 
S,  corresponds  with  that,  S,  of  the  preceding  figure ;  its 
size,  however,  has  greatly  increased,  and  the  intervening 
sensory  tube  has  been  lost ;  its  metameral  opening  at 
the  surface  corresponds  with  that  of  Fig.  62  ;  the  nerve 
supply,  N,  is  now  seen  to  have  secured  a  more  perfect 
relation  to  the  end  organs. 

The  original  significance  of  the  lateral  line  system  as 
yet  remains  undetermined.  As  far  as  can  be  judged  from 
its  development,  it  appears  intimately,  if  not  genetically 
related  to  the  sense  organs  of  the  head  and  gill  region  of 
the  ancestral  fish :  in  response  to  special  aquatic  needs,  it 
may  thence  have  extended  further  and  further  backward 
along  the  median  line  of  the  trunk,  and  in  its  later  differ- 
entiation acquired  its  metameral  characters. 

A  significant  feature  of  its  development  is  its  peculiar 
innervation.  Its  lateral  tract  is  innervated  by  a  specially 
evolved  root  of  the  vago-glossopharyngeal  group,  but  its 
head  region  is  supplied  by  a  similar  root  of  the  facial 
nerve  (perhaps  also  by  the  trigeminus ;  cf.  Collinge,  Ref. 
p.  248). 

In  view  of  this  innervation,  the  precise  function  of  this  en- 
tire system  of  end  organs  becomes  especially  difficult  to  de- 
termine. Feeling,  in  its  broadest  sense,  has  safely  been 


PINEAL  EYE  ^ 

admitted  as  its  possible  use.  Its  close  genetic  relationship 
with  the  hearing  organ  suggests  the  kindred  function  of 
determining  waves  of  vibration.  These  are  transmitted  in 
so  favourable  a  way  in  the  aquatic  living  medium,  that  from 
the  side  of  theory  a  system  of  hyper-sensitive  end  organs 
may  well  have  been  specialized.  The  sensory  tracts  along 
the  sides  of  the  body  are  certainly  well  situated  to  deter- 
mine the  direction  of  the  approach  of  friend,  enemy  or 
prey. 

The  Pineal  Eye 

The  presence  or  absence  in  fishes  of  \hepineal  end  organ, 
the  "unpaired  median  eye  of  chordates,"  may  finally  be 
noted,  since  the  condition  of  the  epiphysis  and  its  associ- 
ated structures  in  fishes  has  an  important  bearing  on 
general  vertebrate  morphology. 

It  is  well  known  that  in  many  forms  of  reptiles  there 
exists,  at  the  distal  end  of  the  epiphysis,  a  well-defined 
sensory  capsule,  whose  structure  shows  unquestionably  its 
optic  function.  It  has  seemed  to  many,  therefore,  that 
throughout  the  chordates  the  epiphysis  has  been  primi- 
tively associated  with  a  median  eye,  which  has  degenerated 
as  the  paired  eyes  became  better  evolved.  That  it  has 
been  retained  in  an  almost  perfect  condition  in  reptiles 
has  accordingly  been  looked  upon  as  an  outcome  of  a 
life  habit  which  concealed  the  animal  in  sand  or  mud, 
and  allowed  the  forehead  surface  alone  to  protrude :  — 
the  median  eye  thus  preserving  its  ancestral  value  in 
enabling  the  animal  to  look  directly  upward  and  backward. 

If  this  view  as  to  the  presence  of  a  parietal  eye  in  the 
ancestral  vertebrate  is  to  be  generally  accepted,  one  would 
naturally  suggest  that  the  organ  should  be  present,  at  all 
events  to  a  recognizable  degree,  in  some  of  the  varied  forms 


54  PINEAL   EYE 

of  the  lowest  vertebrates  extant,  —  fishes  and  amphibia.  If 
there  are  no  suggestions  of  its  visual  nature  among  these 
forms,  one  would  be  inclined  to  believe  with  O.  Hertwig, 
that  the  epiphysis  was  originally  of  a  different  function 
and  that  its  connection  with  a  median  eye  may  have  been 
altogether  of  a  secondary  character. 

The  evidence  as  to  the  presence,  primitively,  of  a  median 
eye  in  fishes  is  certainly  far  from  satisfactory  :  *  in  all  the 
forms  of  recent  fishes,  no  structure  has  been  found  associ- 
ated with  the  epiphysis  which,  by  the  broadest  interpreta- 
tion, could  be  looked  upon  as  suggesting  a  visual  function. 
It  is  possible  that  fishes  and  amphibia  may,  in  their  extant 
forms,  have  lost  all  definite  traces  of  this  ancestral  organ  on 
account  of  some  peculiar  condition  of  their  aquatic  living. 
On  this  supposition,  evidence  of  its  presence  might  be 
sought  in  the  pineal  structures  of  the  earliest  Palaeozoic 
fishes  —  whose  terrestrial  kindred,  and  probable  descend- 
ants, may  alone  have  retained  the  living  conditions  which 
fostered  its  functional  survival. 

It  is  accordingly  of  interest  to  find  that  in  a  number 
of  fossil  fishes  the  pineal  region  retains  an  outward  median 
opening,  whose  shape  and  position  suggest  that  it  may  have 
enclosed  an  optic  capsule.  If  the  median  eye  existed  in 
these  forms,  it  may  well  have  been  passed  along  in  the  line 
of  descent  through  the  early  amphibia  (where  substantial 
traces  of  a  parietal  foramen  occur,  e.g.  as  in  Cricotus)  to 
the  ancestral  reptiles.  This  view  is  greatly  strengthened, 
as  Beard  has  shown,  by  the  presence  in  the  lamprey  of  a 
pineal  end  organ  (optic?). 

The  evidence,  however,  that  the  median  opening  in  the 
head  shields  of  ancient  fishes  actually  enclosed  a  pineal 

*  Hertwig  (Mark),  Handbook  of  Embryology  of  Vertebrates,  and  Cattie,  v. 
Ref.  p.  250. 


PINEAL  EYE 


55 


eye,  is  now  felt  by  the  present  writer  to  be  more  than  ques- 
tionable. The  remarkable  pineal  funnel  of  the  Devonian 
Dinichthys  (Fig.  134)  is  evidently  to  be  compared  with 
the  median  foramen  of  Ctenodus  and  Palcedaphus  (  =  Sire- 
noids,  p.  122)  ;  but  this  can  no  longer  be  looked  upon  as 
having  possessed  an  optic  function,  and  thus  practically 
renders  worthless  all  the  evidence  of  a  median  eye  pre- 
sented by  fossil  fishes.  It  certainly  appeared  that  in  the 
characters  of  the  pineal  foramen  of  Dinichthys  there  ex- 
isted strong  grounds  for  believing  that  a  median  visual 
organ  was  present :  its  opening  was  in  the  pineal  plate, 
midway  between  the  orbits  (PN,  Fig.  134).  At  the  surface 
it  was  of  minute  size  (X,  Fig.  136),  but  below  (Fig.  137) 
it  flared  out  into  a  funnel-like  form,  shown  in  longitudinal 
section  in  Fig.  137  A.  The  peculiar  character  of  this 
opening  seemed  to  render  it  especially  fitted  for  a  visual 
function ;  the  minute  external  opening  forms  an  image 
near  the  plane  of  the  visceral  opening  of  the  funnel,  with- 
out the  specialization  of  a  lens,  —  an  image  so  perfect  that 
it  might  readily  be  photographed.  It  is  evident,  accord- 
ingly, that  if  an  optic  capsule  were  enclosed  by  this  fora- 
men, it  would  have  enabled  its  possessor  to  have  looked 
directly  upward  and  backward ;  and,  without  the  need  of 
developing  lens-like  and  focussing  structures,  it  could  have 
readily  received  the  images  of  all  outer  objects  near  or 
remote. 

But  the  function  of  this  pineal  foramen,  unfortunately 
for  speculation,  could  not  have  been  optical.  It  occurs  in 
a  fish  (Titanichthys)  closely  related  to  Dinichthys,  and, 
as  the  writer  *  has  recently  found,  is  of  a  distinctly  paired 

*  He  is  obliged  by  accumulating  evidence  to  abandon  his  former  view  that 
the  pineal  foramen  of  Dinichthys  contained  a  specialized  optic  capsule  (TV.  Y. 
Rep.  of  Fisheries,  1891,  pp.  310-314). 


^6  PINEAL  EYE 

character,  its  visceral  and  outer  openings  bearing  grooves 
and  ridges  which  demonstrate  that  the  pineal  structures 
must  not  only  have  been  paired,  but  must  have  entered 
the  opening  in  a  way  which  precludes  the  admission  of 
the  epiphysis.  It  is  now,  therefore,  that  the  pineal  fora- 
men which  has  been  described  in  Siluroids  *  becomes 
of  especial  interest,  since  its  contained  structures  are  ap- 
parently connected  with  the  lateral  line  system  of  paired 
nerves. 

It  must  for  the  present  be  concluded,  accordingly,  that 
the  pineal  structures  of  the  true  fishes  do  not  tend  to  con- 
firm the  theory  that  the  epiphysis  of  the  ancestral  verte- 
brates was  connected  with  a  median  unpaired  eye  ;  it  would 
appear,  on  the  other  hand,  that  both  in  their  recent  and 
fossil  forms,  the  epiphysis  was  connected  in  its  median 
opening  with  the  innervation  of  the  sensory  canals  of 
the  head.  This  view,  it  is  now  interesting  to  note,  seems 
essentially  confirmed  by  ontogeny.  The  fact  that  three 
successive  pairs  of  epiphysial  outgrowths  have  been  noted 
in  the  roof  of  the  thalamencephalon,  appears  distinctly 
adverse  to  the  theory  of  a  median  eye. 

*Dean,  N.  Y.  Rep.  of  Fisheries,  1891,  and  Klinckowstrom,  Anat.  Anz., 
1893,  viii,  p.  561. 


Ill 

THE   LAMPREYS   AND   THEIR   ALLIES 

THE  relations  of  the  more  primitive  chordates  to  the 
true  fishes  have  not  been  considered  in  the  present  dis- 
cussion. A  brief  account,  however,  must  be  given  of  the 
Cyclostomes,  or  Marsipobranchii,  which  are  represented  in 
the  recent  lampreys  and  hags. 

The  three  prominent  forms  of  Cyclostomes  are  figured 
on  a  following  page  (Figs.  70-72,  A-D).  They  are  eel- 
like  in  shape,  but  are  lacking  both  in  paired  fins  and  in 
an  under  jaw.  Their  mouth  is  of  a  rounded  form,  and 
is  suctorial ;  when  closing,  its  lateral  margins  draw  to- 
gether. Their  skeleton  is  of  the  simplest  character,  mem- 
branous rather  than  cartilaginous ;  its  elements  are  never 
more  highly  differentiated  than  those  shown  in  the  ac- 
companying figure  (Fig.  69,  A). 

Bdellostoma  is  shown  in  surface  view  in  Figs.  70  and 
72  A,  and  in  sagittal  section  in  Fig.  69.  It  is  looked 
upon  as  the  most  archaic  form  of  the  living  Cyclostomes. 
Barbel-like  structures  surround  its  mouth  region ;  its  nasal 
canal  (Fig.  69,  N  and  C)  has  a  forward  opening  at  the 
snout,  and  a  hinder  one  piercing  the  roof  of  the  pharynx, 
—  a  very  exceptional  character  in  fishes ;  its  tongue,  stud- 
ded with  rows  of  rasp-like  teeth,*  may  be  greatly  everted, 

*  The  teeth  of  Myxinoids  are  cuticular  structures,  and  may  well  have  been 
evolved  within  the  limits  of  the  group.  Beard  has  homologized  them  with  the 
teeth  of  sharks,  but  his  determination  of  the  presence  of  true  enamel  has  not 
been  confirmed  (Ayers). 

57 


THE  LAMPREYS  eg 

as  in  Fig.  72,  A,  and  then  drawn  in  by  stout  tongue 
muscles,  T  (Fig.  69) ;  its  digestive  tube  is  almost  straight, 
terminating  at  the  base  of  the  tail  region  at  A ;  the 
region  of  the  gullet,  OE,  is  pierced  by  a  number  of 
branchial  openings,  varying  from  seven  to  fifteen,  often 
assym metrical.  The  body  cavity  is  an  extremely  large 
one  for  the  size  of  the  contained  viscera.  An  unpaired 
fin,  supported  by  delicate,  unbranched  (dermal)  rays  is 
restricted  to  the  hindmost  part  of  the  body.  Passing 
down  the  side  is  a  row  of  mucous  pouches  by  which  a 
remarkable  supply  of  slime  is  secreted.  The  living  animal 
is  enabled,  by  the  peculiar  character  of  this  slimy  secre- 
tion, to  render  a  pailful  of  water  jelly-like  in  consistency. 

Bdellostoma  occurs  plentifully  in  the  bays  of  the  Pacific 
coast  of  America,  notably  at  Monterey,  California.  It  is 
active  in  its  movements,  is  carnivorous,  and  is  well  known 
to  take  a  baited  hook.  Its  numbers  make  it  an  enemy  of 
the  fishermen,  entangling  and  sliming  their  set  lines,  and 
destroying  the  captured  fish.  It  is  said  to  feed  at  night, 
although  little  is  yet  known  of  its  general  habits  of  living. 
None  but  adult  specimens  have  thus  far  been  observed. 

The  Hagfish,  Myxine  glutinosa  (Fig.  71,  and  72,  7?),  is  in 
many  regards  similar  to  Bdellostoma ;  it  differs  mainly  in 
the  character  of  its  unpaired  fin  and  in  its  branchial  struct- 
ures (Figs.  9,  10).  As  already  noted,  the  outer  ducts  of  the 
gills,  instead  of  opening  separately  at  the  surface  as  in 
Fig.  70,  are  drawn  together  tail-ward,  and  terminate  on 
either  side  in  a  common  ventral  opening  (Fig.  71,  at  the 
point*).  The  unpaired  fin  is  almost  lacking  in  supports; 
its  ventral  origin  is  even  as  far  forward  as  the  branchial 
openings  ;  the  anus,  as  a  slit-like  opening,  pierces  it  in 
the  tail  region.  As  in  Bdellostoma,  the  nasal  canal  begins 
at  the  snout,  and  at  its  hinder  opening  pierces  the  roof  of 


60 


i 


LAMPREYS  AND  HAGS 


61 


the  pharynx ;  this,  with  other  related  conditions,  has  caused 
Myxine  and  Bdellostoma  to  be  included  in  a  sub-group 
of  Cyclostomes,  as  Myxinoids,  or  Hyperotretes*  In  each 
genus  there  is  possibly  no  more  than  a  single  valid  species. 
Myxine  is  a  well-known  form  :  it  occurs  along  the  Atlan- 
tic coast  at  moderate  depths.  It  is  exclusively  carnivorous, 


Fig.  12.  —  A-D.  Ventral  aspects  of  heads  of  (A) 
Bdellostoma  (after  AYERS)  ;  (B)  Myxine  (after  GCJN- 
THER)  ;  (C)  Ammoccetes  (after  GiJNTHER)  ;  (D)  Pe- 
tromyzon  (after  GUNTHER). 

often  boring  its  way  into  the  abdominal 
cavity  of  (diseased  or  injured)  fishes,  and 
with  them  is  brought  to  market;  it  is 
also  taken  not  infrequently  by  line  fisher- 
men. The  smallest  example  that  has 
thus  far  been  described  is  6  cm.  in  length ;  it  was 
recorded  by  Beard.  (V.  Ref.  p.  239). 

The  Lamprey,  Petromyzon,  is  the  most  perfectly  studied 
member  of  the  Cyclostomes.  Its  species  are  common 
to  the  continents  of  the  northern  hemisphere ;  and  in 
South  America  and  Australia  there  occur  very  closely 
allied  genera,  as  Mordacia  and  Geotria.  The  largest 
lamprey,  P.  marinus  (Fig.  72,  and  C,  D\  is  known  to 
attain  a  length  of  nearly  four  feet ;  it  occurs  in  the  coast 

*  v.  Glossary,  p.  228. 


52  THE  LAMPREYS 

rivers,  ascending  them  in  numbers  in  the  springtime 
(April)  on  the  way  to  the  spawning  grounds  (v.  p.  182). 
During  its  adult  life  it  is  supposed  to  be  exclusively  car- 
nivorous, to  some  degree,  perhaps,  parasitic,  although  many 
doubt  that  it  is  truly  parasitic  in  the  sense  of  entering  the 
body  cavities  of  healthy  fishes.  It  certainly  is  often  taken 
attached  to  other  fishes,  as  shark,  sturgeon,  or  salmon. 

Immature  lampreys  differ  so  strikingly  from  the  adults 
that  they  were  formerly  regarded  as  species  of  a  separate 
genus,  Ammoccetes  (v.  p.  215).  In  feeding  habits  the  am- 
moccete  is  widely  unlike  the  mature  form ;  it  is  toothless 
(Fig.  72,  C),  and  in  part  mud-eating,  i.e.  vegetivorous. 

Petromyzon  must  be  regarded  as  the  most  highly  organ- 
ized of  Cyclostomes.  Its  mouth  has  no  longer  the  fring- 
ing barbels  of  Myxinoids, — which  suggest,  according  to 
Pollard,  the  buccal  cirrhi  of  Amphioxus,  —  it  has  acquired 
stout  supporting  cartilages  and  a  funnel-shaped  form, 
studded  with  a  series  of  conical  teeth,  as  shown  in  Fig. 
72,  C.  The  teeth  of  the  hinder  mouth  region  now  appear 
almost  as  though  they  were  supported  by  a  mandibular 
cartilage ;  the  tongue,  as  in  other  Cyclostomes,  bears  the 
teeth  which  are  probably  of  the  greatest  functional  impor- 
tance. The  nasal  canal  of  Petromyzon  has  its  outer  opening 
on  the  dorsal  surface  of  the  head  ;  its  inner  end,  however, 
does  not  perforate  the  roof  of  the  mouth,  although  produced 
backward  as  a  blind  sac,  closely  apposed  to  the  pharynx. 
Petromyzonts  are,  accordingly,  arranged  as  the  sub-group 
Hyperoartia,  in  contrast  to  the  Myxinoids. 

Further  structural  characters,  which  the  lamprey  seems 
to  have  derived  from  simpler  conditions,  may  be  noted  in 
its  unpaired  fin,  gill  chamber,  nervous  system,  and  skele- 
ton. The  unpaired  fin  has  subdivided  into  dorsal  and 
caudal  elements,  and  is  now  supported  by  well-marked 


AFFINITIES   OF  LAMPREYS  63 

rays,  which  (sometimes)  bifurcate.  The  branchial  region  of 
the  adult  lamprey's  gullet  is  restricted  to  a  pouch-like 
diverticulum  (v.  p.  263  and  Fig.  326).  A  'sympathetic' 
nervous  system,  and  a  '  lateral  line '  has  appeared  :  the 
latter  passes  down  the  side  in  two  branches,  one  above 
and  one  below  the  median  lateral  plane  :  its  end  organs 
are  the  pouches  of  nervous  epithelium  which  in  Myxi- 
noids  are  scattered  generally  over  the  body  surface.  The 
skeletal  structures  of  the  lamprey  (Fig.  69,  A)  indicate 
well-marked  advances :  a  stouter  supporting  tissue  of  car- 
tilage-like character  has  appeared ;  the  brain  case  is  partly 
roofed  over  ;  neural  processes,  NPt  a  branchial  basket, 
BB,  and  a  series  of  mouth  cartilages  are  especially  note- 
worthy. 

Affinities  of  the  Cyclostomes 

The  relations  of  the  group,  Cyclostomi,  to  the  earlier 
chordates,  and,  on  the  other  hand,  to  fishes,  have  been  by 
no  means  definitely  established.  Dohrn  and  others  have 
suggested  that  the  Cyclostomes  are  greatly  degenerate,  and 
are  even  closely  akin  to  the  recent  bony  fishes,  as  perch 
or  cod.  Their  views  have  been  based  upon  several  struct- 
ural characters,  notably  vestigial  organs,  such  as  the  ap- 
pendages at  the  sides  of  the  cloacal  opening  of  Petromyzon 
which  were  believed  to  represent  pelvic  fins ;  and  there  was 
further  taken  into  consideration  the  belief  that  the  entire 
group  was  one  of  degenerate  life  habits.  The  views  of  these 
writers,  however,  do  not  appear  to  be  confirmed  by  later 
studies,  and  the  belief  is  becoming  more  and  more  general 
that  Cyclostomes  represent  a  very  ancient  chordate  stem 
whose  ancestral  form  is  most  nearly  exemplified  by  Bdel- 
lostoma.  Parasitism  has  been  acquired  to  a  limited  degree, 
but  does  not  appear  to  have  affected  the  general  characters 


64  KINSHIPS   OF  CYCLOSTOMES 

of  the  group.  Among  its  primitive  features  are  to  be  in- 
cluded :  skeleton  and  muscles,  continuous  vertical  fin,  gill 
characters  (p.  260),  viscera  (p.  263),  urino-genital  organs 
(pp.  266,  270),  nervous  and  circulatory  systems  (pp.  260, 
269,  and  274).  With  these  must  be  taken  into  account: 
absence  of  mandible*  and  of  paired  fins  and  girdles;  and  in 
addition  the  remarkable  conditions  of  metamerism  (p.  14). 

Little  more  that  a  vague  kinship  between  lampreys  and 
fishes  has  been  established  by  the  study  of  living  forms. 
And,  on  the  other  hand,  it  would  appear  equally  impracti- 
cable to  obtain  evidence  bearing  upon  this  problem  from 
the  side  of  palaeontology.  All  that  is  known  of  the  recent 
Cyclostomes  more  than  suggests  that  their  soft  body  struct- 
ures would  prove  most  unfavourable  to  fossilization.  It 
would  be  only,  therefore,  in  the  event  of  some  of  their 
ancient  members  possessing  calcified  structures  that  palae- 
ontology would  be  able  to  offer  a  clue  as  to  their  ancient 
affinities. 

Upon  the  problem  of  their  descent  the  evolution  of 
fishes  has,  however,  an  undoubted  bearing,  in  suggesting 
the  lines  and  effects  of  aquatic  evolution  and  the  perma- 
nence of  generalized  types.  It  certainly  tells  of  the  ex- 
treme slowness  of  the  evolution  of  aquatic  forms  and  con- 
vinces us  that  the  ancestral  Cyclostome  could  only  have 
occurred  in  a  time  stratum  exceedingly  remote.  Palaeon- 
tology cannot  perhaps  hope  to  obtain  more  than  sugges- 
tions of  the  ancestral  forms,  although  these,  from  their 
generalized  characters,  may  well  have  survived  during  geo- 

*  The  cartilages  of  the  mouth  region  of  Cyclostomes  have  been  homologized 
with  the  structures  of  gnathostomes  ;  Pollard  recently  (Anat.  Anz.  ix,  pp. 
349-359)  ascribes  a  cirrhostomial  origin  to  the  mouth  parts  of  a  Teleostome 
(catfish),  which  the  writer  cannot  believe  has  been  demonstrated;  variations 
in  the  number,  shape,  and  function  of  the  cartilages  of  the  mouth  rim  of 
Cyclostomes  might  well  have  occurred  within  the  limits  of  this  ancient  group. 


A   FOSSIL  LAMPREY  65 

logical  ages.  It  can,  however,  show  that  Cyclostomes  are 
not  the  degenerate  descendants  of  shark-like  forms ;  and 
—  if  only  by  analogies  in  the  evolution  of  fishes  —  it  may 
still  be  able  to  demonstrate  with  fair  probability  their 
genetic  kinships.  It  may,  for  example, 
prove  that  in  the  most  ancient  time  there 
existed  undoubted  Cyclostomes,  and  that 
these  in  many  and  most  specialized  forms 
were  even  then  branching-off  twigs  of  a 
great  descent  tree.  In  such  an  event  an 
inference  would  certainly  be  the  more 
reasonable  which  derived  the  advancing 
line  of  fish  descent  from  the  genealogical 
tree  of  the  more  primitive  Cyclostomes, 
than  that  vice  versa. 

It  is  now  accordingly  of  especial  inter- 
est that  the  fossil  remains  of  what  seems 
undoubtedly  a  lamprey  (Fig.  73)  have  been 
discovered  in  the  Devonian ;  and  this,  to- 
gether with  a  better  knowledge  of  the 
ancient  and  curious  chordate  group,  Os- 
tracoderms,  may,  it  is  hoped,  lead  to  some 
solution  of  the  Cyclostome  puzzle. 


The  Ostracoderms 


Fig.  73.  —  The  De- 
vonian Cyclostome, 
Palaospondylus  gunni, 
T.  X  4.  (After  TRA- 

Ostracoderms,  as  they  are  called  from  QUAIR.)     Achanarras 

quarry,  N.  Scotland. 

their  shell-like,  dorsal  and  ventral  derm 
plates,  are  certainly  the  oldest  known  remains  of  verte- 
brates.*    In  their  simpler  forms  they  occur  in  the  Upper 
Silurian ;  they  flower  out  in  a  variety  of  types  in  the  De- 
vonian, and  shortly  become  extinct.     In  the  present  con- 

*  The  earlier  (Ordovician)  vertebrate  remains  described  by  Walcott  are  as 

yet  uninterpretable. 
F 


FIG.  74 


Figs.  74-79.  —  Pteraspis  (restored) .  X  5.  (After  LANKESTER.)  Lower  Old  Red 
Sandstone,  Herefordshire.  75.  Palceaspis  americana,  Claypole.  X  4.  (Restoration  after 
CLAYPOLE,  somewhat  modified  by  the  writer.)  76.  Pteraspis,  dorsal  shield,  slightly 
restored.  (After  LANKESTER.)  77.  Pteraspis,  ventral  shield  ("  Scaphaspis  ") ,  showing 
mucous  canals.  (After  SMITH  WOODWARD.)  78.  Cephalaspis  lyelli,  side  view.  (Re- 
stored by  LANKESTER.)  79.  Cephalaspis  lyelli,  dorsal  aspect.  X  5.  (After  L.  AGASSIZ.) 
Specimen  from  Old  Red  Sandstone,  Forfarshire.  A  C.  Rhomboidal  scales  from  different 
body  regions.  B.  Tessera  from  middle  layer  of  head  shield. 

66 


OSTRA  CODERMS 


67 


nection  they  may  be  described,  if  only  to  indicate  that 
they  are  in  no  way  closely  connected  with  the  ancient 
shark  types  (p.  78),  and  that  they  are  accordingly  of  but 
indirect  interest  in  the  descent  of  jaw-bearing  vertebrates. 

Ostracoderms  may  readily  be  reduced  to  three  general 
types,  Pteraspid,  Cephalaspid,  and  Pterichthid.  The  first, 
oldest,  and  probably  simplest  occurs  in  the  Lower  Old 
Red  Sandstone  of  Herefordshire.  It  was  provided  with 
arched  back  and  breastplate  (Figs.  74,  76,  77),  from  whose 
anterior  lateral  notches  a  pair  of  eyes  protruded ;  the  sur- 
face of  these  plates  (Fig.  77)  appears  to  have  been  grooved 
for  sensory  canals.  Pteraspis,  as  seen  in  the  restoration, 
had  a  snout  plate,  a  dorsal  spine,  and  a  body  casing  of 
rhomboidal  scales ;  its  mouth  was  probably  in  the  region 
immediately  below  the  eyes,  in  front  of  the  margin  of  the 
well-rounded  ventral  plate ;  this  was  generally  regarded  as 
the  dorsal  plate  of  a  kindred  genus,  " Scaphaspis"  Closely 
related  is  the  American  Pteraspid,  Palceaspis  (Claypole), 
from  the  Upper  Silurian  of  Pennsylvania  (Fig.  75) ;  this 
form  lacks  the  dorsal  spine  of  the  English  species  ;  it  has  a 
well-marked  lateral  plate  intervening  between  those  of  the 
back  and  ventral  side,  and,  according  to  its  discoverer, 
Professor  Claypole,  possessed  pectoral  fins  similar  to  those 
seen  in  Fig.  123.  Its  hinder  trunk  region  is  unknown. 

Cephalaspis,  the  second  type  of  Ostracoderm,  is  from 
the  Old  Red  Sandstone  of  Scotland  (Figs.  78,  79).  It  was 
curiously  suggestive  of  a  trilobite,  and  with  little  doubt 
mimicked  this  ancient  crustacean  in  its  life  habits.  Its 
most  prominent  feature  is  a  crescent-shaped  head,  with 
sharp  rounded  margin  like  a  saddler's  knife.  This  is 
protected  dorsally  by  but  a  single  plate,  arching  upward 
and  backward ;  at  its  summit  was  a  pair  of  closely  apposed 
eyes,  and  near  its  flattened  rim  were  pouch-like  sensory 


Fig.  80 


SL 


Figs.  80-82. — Pterichthys  testudinarius,  Ag. ;  restored  by  R.  H.  TRAQUAIR,  from  the 
dorsal  aspect  (80),  ventral  aspect  (8i),and  lateral  aspect  (82).  The  double  dotted  lines 
indicate  the  grooves  of  the  sensory  canal  system ;  and  in  the  trunk,  the  thick  lines  repre- 
sent the  exposed  borders  of  the  plate,  the  thin  line  showing  the  extent  of  the  overlap. 

ADL.  Anterior  dorso-lateral.  AMD.  Anterior  median  dorsal.  A  VL.  Anterior  ventro- 
lateral.  EL.  Extra-lateral  (or  operculum).  L.  Labial.  MOCC.  Median  occipital.  PM. 
Premedian.  PDL.  Posterior  dorso-lateral.  PMD.  Posterior  median  dorsal.  PVL.  Pos- 
terior ventro-lateral.  SL.  Semilunar.  (Figure  from  SMITH  WOODWARD.) 

68 


PTERICHTHYS  AND    CEPHALASPIS 


69 


organs.  The  angles  of  the  head  plate  are  in  some  genera 
produced  most  acutely,  and  bear  spines  which  served  prob- 
ably in  progression.  The  body  walls  were  encased  in 
metameral  derm  plates,  which  became  arched  in  the 
median  line  to  serve  as  a  dorsal  fin.  A  heterocercal  tail 
and  an  anal  fin  were  also  present.  Problematical  opercu- 
lar  flaps  protruded  at  the  sides  of  the  head  plate,  and 
represented  (as  is  now  known)  a  continuation  of  the  elastic 
middle  layer  of  the  head  plate. 

Pterichthys  must  be  looked  upon  as  the  culminating 
type  of  these  anomalous  forms  (Figs.  80-82).  As  in  some 
Cephalaspids,  there  are  two  body  regions  that  are  cui- 
rassed, — head  and  thorax.  The  tail  portion  is  encased 
in  dermal  plates;  it  bears  a  dorsal  *  fin  and  a  clumsy 
heterocercal  tail.  In  the  consolidation  of  its  armoured 
parts  the  elements  are  usually  clearly  indicated.  The 
curious  arm-like  jointed  appendages  at  the  lateral  head 
angle  were  formerly  regarded  as  homologous  with  the 
opercular  flaps  of  Cephalaspid,  but  are  now  known  to  be 
nothing  more  than  the  lateral  head  angles  produced  and 
specialized  (i.e.  jointed  for  locomotion).  The  strengthen- 
ing spine  of  the  dorsal  fin  is  also  but  a  primitive  speciali- 
zation of  the  body  integument ;  it  is  formed  by  a  pair  of 
the  bent  scales  of  the  dorsal  ridge,  and  is  not,  therefore, 
homologous  with  the  radial  fin  cartilages  of  fishes. 

In  Cephalaspids  and  Pterichthids  there  occurs  a  pineal 
plate  (or  its  equivalent)  which  may  have  been  either 
movable  or  fixed.  In  this  are  to  be  found  the  paired  eyes 
and  the  socket  of  a  median  unpaired  eye  (?).  In  all  of 
these  singular  forms  mouth  parts  *  are  wanting.  In 

*  Smith  Woodward  has  since  described  a  pair  of  inturned  labial  plates  in 
the  mouth  of  Pterichthys.  Their  position  suggests  that  the  sides  of  the  mouth 
rim  might  become  apposed,  as  in  the  Cyclostomes. 


70  KINSHIPS   OF    OSTRACODERMS 

no  instance  has  a  trace  of  endoskeletal  parts  been  ob- 
served. 

The  more  that  is  determined  of  the  structural  characters 
of  Ostracoderms,  the  less  is  it  possible  to  accept  the 
views  as  to  their  affinities  with  forms  other  than  "fishes," 
either  (Cope)  as  to  their  permanent  larval-ascidian  char- 
acters, or  (Patten)  as  to  their  relationships  with  arachnids. 
Their  general  kinship  is  certainly  to  the  fishes.  Accord- 
ing to  Smith  Woodward,  the  markings  appearing  on  the 
visceral  surface  of  head  tests  indicate  the  presence  of 
gill  pouches ;  in  some  forms  clearly  marked  furrows  sug- 
gest the  possession  of  vertical  semicircular  canals ;  fish-like 
sense  organs  occur  (Fig.  77) ;  and  their  derm  plates,  in 
their  cancellated  atid  bone-like  characters,  cannot  well  be 
likened  to  the  exoskeletal  parts  of  invertebrates. 

The  lamprey-like  form,  Palceospondylus  gunni,  Traquair 
(Fig.  73),  in  the  Lower  Devonian  is  by  many  looked  upon 
as  the  actual  solution  of  the  Cyclostome,  and  even  of  the 
Ostracoderm  puzzle.  This  interesting  fossil  was  discov- 
ered by  Dr.  Marcus  Gunn,  in  the  Lower  Old  Red  Sand- 
stone of  Caithness,  and  was  described  in  several  papers  by 
Traquair  (Trans.  Edin.  Soc.,  1892-1894).  It  is  of  very 
small  size,  commonly  of  about  an  inch  in  length,  but  is 
admirably  preserved  (Fig.  73).  There  can  be  no  doubt 
that  Palaeospondylus  possessed  a  ring-like  mouth  sur- 
rounded by  barbels  like  those  of  a  Myxinoid,  and  that  it 
lacked  paired  fins.  But  as  a  Cyclostome  it  must  have 
highly  specialized,  having  the  same  relation  to  the  more 
primitive  Cyclostomes  of  its  day,  as  had  the  minute  Acan- 
thodians  (p.  81)  to  the  existing  sharks.  It  had  thus  a 
remarkably  large  caudal  fin  with  elaborately  bifurcating 
supports ;  it  had  evolved  stout,  ring-like  vertebrae,  even  in 
the  caudal  region,  which  had  developed  stout  neural  proc- 


PAL&  OSPOND  YLUS  7  r 

esses.  Its  skull  was  highly  evolved  :  in  its  anterior  part 
were  represented,  according  to  Traquair,  the  palatine  car- 
tilages ;  the  brain  case  was  complete,  and  the  auditory 
capsules  were  of  relatively  enormous  size.  The  lateral 
plates  of  the  neck  region  are  as  yet  uninterpretable. 

From  the  evidence  of  Palaeospondylus,  accordingly,  it 
may  reasonably  be  inferred  that  lamprey-like  forms  existed 
in  highly  specialized  conditions,  even  at  the  beginning  of 
Devonian  times.  If  they  then  existed,  it  is  of  course  not 
impossible,  and  perhaps  even  not  improbable,  that  their 
offshoots  may  have  culminated  in  the  Ostracoderms,  as 
Smith  Woodward  has  suggested.  These  can  certainly 
belong  to  no  gnathostome  stem.  Their  organs,  though 
often  highly  specialized,  were  yet  of  the  most  primitive 
order, — lack  of  paired  appendages,*  softness  of  axial  parts, 
lowly  sense  organs;  even  the  dermal  plates,  elaborate  in 
their  subdivision  or  ornamentation,  or  in  the  special  uses, 
as  "opercula,"  "pectoral  fins,"  or  "  fin  rays,"f  are  yet  but 
primitive  specializations  of  the  exoskeleton. 

*  The  presence  of  paired  fins  in  Palaeaspis,  as  determined  by  Claypole,  has 
not  been  confirmed.  The  present  writer,  to  whom  the  type  specimens  were 
kindly  shown  by  their  describer,  must  regard  these  structures  as  elasmo- 
branchian  (Chimseroid?)  spines,  in  crushed  condition,  accidentally  associated 
with  the  head  region  of  the  fossil. 

t  It  is  obvious  that  these  structures  are  but  analogous  to  the  opercular  and 
fin  structures  of  fishes,  and  would  tend  to  separate,  rather  than  closen,  the 
ties  of  kinship  of  these  groups. 


IV 

THE    SHARKS 

ALL  true  fishes  may  conveniently  be  grouped  into  the 
four  sub-classes  that  have  been  noted  (p.  8)  in  the  introduc- 
tory chapter.  These  are  now  in  turn  to  be  considered,  and 
in  this  review  the  principal  forms,  fossil  and  recent,  of  each 
group  must  be  exemplified.  From  the  standpoint  of  their 
structural  and  developmental  characters,  a  general  idea  of 
the  mutual  relationships  of  the  fishes  may  finally  be 
deduced. 

The  sub-class  Elasmobranchii,  which  includes  the  sharks 
and  rays,  is  usually  regarded  as  representing  most  nearly 
the  persistent  ancestral  condition  of  fishes,  and,  indeed,  of 
all  other  jaw-bearing  vertebrates.  As  a  group  it  should 
certainly  be  taken  first  in  the  present  discussion,  as  a  con- 
venient basis  of  comparison. 

Sharks  and  rays  should  be  looked  upon  at  the  beginning 
as  the  representatives  of  the  oldest,  most  widely  diffused, 
and  possibly  largest  group  of  fishes.  In  their  living 
forms  they  suggest  but  faintly  the  number  and  variety  of 
their  fossil  kindred.  It  is  generally  thought  that  the  his- 
tory of  this  group,  when  more  perfectly  determined,  is  to 
furnish  the  most  important  evidence  as  to  the  general 
lines  of  descent  of  the  fishes. 

72 


73 


74  STRUCTURES   OF  SHARKS 

Structural  Characters 

The  definition  of  a  shark  emphasizes  its  cartilaginous 
skeleton,  investiture  of  shagreen,  uneven  (heterocercal)  tail, 
and  its  separate  and  slit-like  gill  openings.  Its  more  defi- 
nite characters  may  well  be  summarized  in  the  accompany- 
ing figure  (Fig.  83). 

I.  The  SKELETON  is  cartilaginous  (cf.  Fig.  83,  84,  and 
p.  252),  sometimes  calcified  generally,  but  always  (in  recent 
forms)  lacking  in  dermal  bones.  Behind  the  simple,  trough- 
like  brain  case  the  vertebral  rod,  beginning  at  the  occip- 
ital condyles,  is  clearly  segmented  ;  the  notochord  is  often 
retained,  especially  in  the  tail  region,  NC,  but  is  encroached 
upon  by  the  cartilaginous  rings,  centra,  C,  arising  metamer- 
ally  in  its  sheath  (Fig  85).  The  vertical  supports  of  each 
centrum  include  a  well-marked  ventral  plate,  the  haemal 
arch  and  spine,  HER, — which' in  the  tail  region  probably 
represents  as  well  the  cartilaginous  elements  of  the  fin 
support,  —  and  a  pair  of  small  dorsal  plates,  the  neurals 
and  interneurals,  NP,  1C,  each  capped  by  a  neural  spine, 
NS.  The  fin  supports  compare  closely  in  structure  with 
the  vertebral  processes ;  they  form  a  large  part  of  the 
functional  fin,  and  preserve  clearly,  both  in  basal  and 
radial  parts,  thpr  metameral  character.  This  -segmental 
arrangement  is  also  characteristic  of  the  supporting  ele- 
ments of  the  cavity  of  the  mouth  and  throat.  These  con- 
stitute the  " visceral  arches"  (cf.  p.  256)  which  pass 
backward  from  the  rim  of  the  mouth  to  the  region  of  the 
pectoral  fin.  The  first  visceral  arch  strengthens  the  rim  of 
the  mouth  ;  it  is  margined  with  teeth  and  functions  as  jaws,* 

*  The  writer  believes  that  the  upper  element  of  the  mandibular  arch  is  to 
be  regarded  as  the  palatoquadrate  cartilage,  rather  than  the  pre-spiracular 
ligament. 


75 


76  STRUCTURES   OF  SHARKS 

P  and  M.  The  second  arch  serves  as  the  principal  support 
of  the  jaw  hinge,  HM,  while  holding  in  position,  ventrally, 
the  hinder  arches;  it  also  supports  the  tongue,  and  forms 
the  hinder  border  of  the  spiracle  (p.  19).  The  succeeding 
arches,  usually  five  in  number,  are  the  bearers  of  the  func- 
tional gills,  their  jointed  structure  permitting  the  dilating 
and  contracting  movements  of  breathing. 

As  a  further  skeletal  element  of  the  Elasmobranchs  the 
sub-notochordal  rod  is  to  be  mentioned.  It  is  present  in 
the  larval  stages  of  sharks,  and  appears  to  persist  in  the 
adult  Cladoselache  (p.  79).  It  is  a  prominent  structure 
of  the  hinder  body  region,  passing  along,  like  a  second 

notochord,  immediately  below  the 
vertebral  axis.  Its  significance  is 
unknown. 

II.    The     INTEGUMENT     of    the 
sharks,  as  has  been  noted  (p.  23), 
is  studded  with  shagreen  denticles, 
FiS-    85.  —  Vertebrae   of     often   in  metameral   arrangement. 

shark  (Squatina)  ,  longitudinal 

section.    (After  ZITTEL  )  These  have  been  shown  to  corre- 


"pond  dearly  with  the  teeth. 

centrum.      iv.    Intervertebral  The  Soft  Structures  characteristic 

space,     w.  Centrum.  . 

of  the  Elasmobranchs  include  :  — 

III.  GILLS,  arranged    metamerally   (p.    19)  ;    the    most 
anterior  one  partly  functional  in  the  spiracle,  SP. 

IV.  SENSE   ORGANS   OF   THE   LATERAL   LINE,    in  some 
forms  in  an  open  sensory  groove,  in  others   sunken  and 
constricted  in  metameral  pouches. 

V.  BRAIN,    simple    in    its    segmental    characters    and 
cranial  nerves  (v.  p.  274). 

VI.  NASAL  ORGAN,  EYE  AND  EAR,  as  shown  on  p.  276. 

VII.  RENAL  AND  REPRODUCTIVE  SYSTEMS  (p.  270),  ab- 
dominal pores  (p.  271). 


FOSSIL   SHARKS  jj 

VIII.  DIGESTIVE  TUBE  with  a  single  bend,    5,   /,    the 
intestine   provided  with  a  spiral  valve  (p.  263),  terminat- 
ing, together   with   the  ducts  of   the  renal  and  reproduc- 
tive organs,  in  a  common  cloaca,  CL  (p.  266).     Liver,  Z, 
spleen,  and  pancreas  large ;  mesenteries  simple  but  greatly 
fenestrated  ;  air  bladder  absent. 

IX.  HEART  with  a  contractile  arterial  cone,  CA,  con- 
taining several  rows  of  valves  (p.  260) ;  circulatory  system 
in  general  as  described  on  p.  269. 

X.  "  CLASPERS  "  developed   at    the    hinder    margin  of 
the  ventral  fins  as  the   intromittent   organ  of   the  male. 
They  are  rudimentary  in  the  female,   CL'.      Each  clasper 
is  the  trough-like  hinder  rim  of  the  fin,  which  becomes 
transformed  into  the  compact,  elongated,  tube-like  sperm 
canal.     Its  tip  is  often  studded  with  elongated  shagreen 
denticles  whose  recurved  cusps  retain  it  in  copulo. 

Fossil  Sharks 

Of  all  fishes,  sharks  certainly  suggest  most  closely  in 
their  general  structures  the  metameral  conditions  of  the 
Cyclostome :  it  should  also  be  noted  that  they  possess  the 
greatest  number  of  body  segments,  in  some  instances 
over  three  hundred,  known  among  vertebrates.  Little  is 
known,  however,  of  the  primitive  stem  of  the  sharks,  and 
even  the  lines  of  descent  of  the  different  members  of  the 
group  can  only  be  generally  suggested.  The  development 
of  the  recen£  forms  has  yielded  few  results  of  undoubted 
value  to  the  phylogenist :  it  would  appear  as  if  palaeon- 
tology alone  could  solve  the  puzzles  of  their  descent. 

The  history  of  fossil  sharks  has  as  yet  been  but  imper- 
fectly outlined.  The  remains  of  the  more  ancient  forms 
have  usually  proven  so  imperfectly  preserved  that  little 
could  be  determined  of  their  structural  characters.  Spines, 


7g  PALEOZOIC  SHARKS 

teeth,  shagreen  denticles,  have  proven  the  antiquity  of  the 
shark  stem  and  the  wealth  and  variety  of  its  fossil  forms ; 
they  have  provided  the  evidence  that  even  in  Silurian 
times  there  lived  sharks  whose  exoskeletal  specializa- 
tions had  progressed  further  than  in  their  recent  kindred  : 
that  in  the  Carbon  there  occurred  the  culminating-point 
in  their  differentiation,  when  specialized  sharks  existed 
whose  varied  structures  are  paralleled  only  by  those  of 
existing  bony  fishes,  —  sharks  fitted  to  the  most  special 
environment ;  some  minute  and  delicate  ;  others  enormous, 
heavy,  and  sluggish,  with  stout  head  and  fin  spines,  and 
elaborate  types  of  dentition. 

But  the  detached  fragments  of  the  fossil  sharks  can  give 
little  satisfactory  knowledge  of  their  general  structures. 
The  simpler  the  form  of  the  shark,  indeed,  the  less  liable 
is  it  to  become  fossilized.  The  more  generalized  of  the 
ancient  sharks  must  thus  remain  structurally  unknown 
until  more  perfect  fossils  come  to  be  found.  To  this  event 
the  discoveries  of  the  past  few  years  have  certainly  yielded 
most  encouraging  aid.  Several  forms  of  sharks  of  the 
Lower  Carbon  and  Permian  have  been  obtained  in  a  con- 
dition of  admirable  preservation,  and  have  already  con- 
tributed materially  to  the  morphology  of  Elasmobranchs. 
Other  early  forms  may  be  forthcoming  which  will  be  found 
to  have  retained  sufficient  of  the  characters  of  their  an- 
cestors to  warrant  more  definite  views  as  to  the  general 
relationships  of  fishes. 

Of  the  three  primitive  forms  of  fossil  sharks  lately 
described :  the  earliest,  from  the  Ohio  Waverly  (Lower 
Carbon)  is  Cladoselache,  Dean  ;  a  later  and  puzzling  form, 
from  the  Carboniferous,  is  Chondrenchelys,  Traquair ;  the 
latest  from  the  Permian  and  Coal  Measures,  is  Pleiiracan- 
tkus,  Agassiz.  The  only  early  shark  type  that  had  previ- 


CLADOSELACHE 


79 


ously  been  structurally  known  was  that  of   the  aberrant 
and  highly  specialized  Acanthodian  of  the  Coal  Measures. 

Cladoselache  is  the  most  primitive,  as  well  as  the  oldest, 
of  these  ancient  sharks.  It  is  relatively  of  small  size, 
varying  in  the  length  of  its  species  from  two  to  six  feet. 
Its  outward  form,  as  restored  by  the  writer,  is  seen  in  Fig. 
86,  and  in  ventral  view  in  Fig.  86  A.  The  shape  is  clearly 


Fig.  86.  —  Cladoselache  fyleri,  Newb.    X  $.    Restoration  by  writer.    After  speci- 
men in  the  museum  of  Columbia  College  from  Cleveland  shales,  Ohio. 
Fig.  86  A.  —  Cladoselache  fyleri ;  ventral  aspect. 

that  of  a  modern  shark;  the  fins,  too,  in  their  size  and 
position,  have  somewhat  of  a  modern  look ;  and  at  the 
base  of  the  tail  occurs  the  small  horizontal  keel  of  many 
living  forms.  But  in  spite  of  these  peculiarities,  Cladose- 
lache must  be  looked  upon  as  the  most  archaic,  and,  in 
many  ways,  the  most  generalized  of  known  sharks ;  its 
paired  fins  are  but  the  remnants  of  the  lateral  fold  (p.  43), 
serving  alone  as  balancers ;  the  tail,  curiously  specialized, 
is  widely  heterocercal,  its  hinder  web  lacking  supports  in 
the  upper  lobe  (p.  36) ;  the  vertebral  axis  is  notochordal ; 


go  CLADOSELACHIAN  SHARKS 

and  the  writer  now  finds  that  an  exceedingly  simple  con- 
dition existed  in  the  neural  and  haemal  arches  ;  they  prove 
to  be  of  moderate  size  and  thickness,  each  a  tapering  rod 
of  cartilage,  forked  at  its  base ;  each  body  segment  con- 
tains a  single  neural  and  haemal  spine,  closely  alike  in  size. 
Unlike  modern  sharks,  Cladoselache  was  without  claspers  : 
its  eggs  must  have  been  fertilized  after  their  deposition,  as  in 
the  majority  of  fishes  other  than  Elasmosbranchs.  The  gill 
openings,  at  least  seven  (probably  nine)  in  number,  appear 
as  in  the  restoration,  to  have  been  shielded  anteriorly  by 
a  dilated  dermal  flap.  A  spiracle  was  probably  present. 
The  jaws  were  slender,  and  apparently  hyostylic  (p.  257) ;  * 
the  teeth  are  of  the  pattern  of  shagreen  denticles,  but  occur 


Fig.  86  B.  —  Teeth  of  ("  Cladodus")  Cladoselache.  X  £.  The  above  forms 
occur  in  different  regions  of  the  mouth. 

in  clusters  (^Cladodus"  Fig.  86,  B).  The  mouth  was  ter-  . 
minal  in  its  position.  The  nasal  capsule  was  apparently 
not  connected  with  the  mouth  by  a  dermal  flap.  The  eye 
was  protected  by  several  rings  of  rectangular  plates,  clearly 
shagreen-like  in  character.  The  integument  was  finely 
studded  with  minute  lozenge-shaped  denticles,  and  was 
everywhere  lacking  in  membrane  bones.  The  lateral  line 
retained  its  groove-like  character. 

The  shark,  Acanthodes  (Fig.  87),  of  the  Coal  Measures 
is  now  to  be  regarded  (Smith  Woodward)  as  a  member  of 
a  highly  specialized  Palaeozoic  group.  And  its  many  spe- 
cialized structures  —  added  to  its  greatly  reduced  size  — 

*  As  Claypole's  recent  figure  seems  to  demonstrate.     Am.  Geol.^Jan. 


ACANTHODES 


81 


may,  perhaps,  have  been  the  cause  of  its  extinction. 
The  present  writer  believes  that  Cladoselache  may  well 
have  represented  the  ancestral  form  of  the  Acanthodian. 
The  generalized  structures  of  the  former  have  given  place 
to  a  perfected  dermal  armouring,  and  a  completed  series 


Fig.  87.  —  Acanthodes  wardi,  Egert.     X  about  J.     (Restoration  slightly  modified 
after  SMITH  WOODWARD.)     Coal  Measures,  England. 

of  balancing  fins.  In  Acanthodes  the  shagreen  denticles 
have  thus  become  greatly  enlarged  and  thickened,  their 
flattened  and  enamelled  surfaces  wedging  closely  to- 
gether (Fig.  88) ;  and  on  the  roof  of  the  head  and 
mouth  traces  of  membrane  bones  have  appeared.  Around 


'Pig.  88.— Acanthodes gracilis,Eeyr.    Shagreen.    X  about  i£ff.     (After  ZlTTEL.) 
a.  Outer  face.     b.  Inner  face.     c.  Isolated  denticle. 

the  eyes  the  many  shagreen  plates  of  Cladoselache  have 
fused  into  a  group  of  four.  Supporting  the  dermal  gill 
frills,  there  have  also  appeared  rows  of  minute  sculptured 
plates  (corresponding,  perhaps,  to  those,  BR,  of  Fig. 
145),  homologous,  apparently,  with  shagreen  denticles. 


82 


ACANTHODIAN  SHARKS 


Further  resemblances  to  Cladoselache  are  to  be  traced  in 
the  position  of  the  fins,  gill  slits,  eyes,  mouth,  nasal  cap- 
sule, and  in  the  structures  of  the  caudal  fin  (Kner),  and  of 
the  lateral  line.     The  teeth,  however,  are  no  longer  of  the 
derm-denticle  pattern ;  they  have  become  few  in  number, 
large,  and  "degenerate"  in  their  fibrous  structure  (Fig. 
88,  A}.     The  fins  are  clearly  more  per- 
fect balancing   organs  than  those  of 
the  older  shark  ;  their  anterior  rim  is 
Fig.  88  A. -Teeth  of    formed  by  a  stout  spine,  representing, 
Acanthodopsis  wardi.  x  i.     the  present  writer  believes,  the  con- 

From   sketch   after    speci- 
men in  British  Museum.        cresccnce  of  the  radial  fin  supports  ; 

it   is   heavily  crusted   over  with  the 

calcifications  of  shagreen  denticles.  The  functional  fin 
area  has  thus  become  dermal,  and  is  lacking  in  supports, 
excepting  in  the  pectoral  fin.  This,  as  the  most  highly 
specialized  of  all  the  body  fins  (p.  41),  appears  in  some 
cases  to  have  evolved  strengthening  (dermal)  jays  in  its 
proximal  portion  (as  in  Figs.  87  and  32). 


Fig.  89.  —  Climatius  scutiger,   Egert.     X  i.     (From   ZlTTEL,  after   POWRIE.) 
Old  Red  Sandstone,  Forfarshire. 


In  connection  with  these  fin  structures  the  remarkable 
Acanthodian,  Climatius  (Fig.  89),  should  finally  be  men- 
tioned. In  this  form  the  paired  fins  are  represented  by  a 
series  of  fin  spines  whose  size  grades  backward  from  the 
pectoral  region ;  a  series  of  paired  fins  appear,  therefore, 


PLE  URA  CAN  THUS 

to  have  been  present, 
and  suggest  strongly 
continuous  fin-fold  char- 
acters. (V.  p.  40.) 

Pleuracanthus  (Fig. 
90),  the  third  of  the 
well  -  known  Palaeozoic 
sharks,  is  widely  differ- 
ent from  the  Acantho- 
dian :  it  suggests  a  tran- 
sitional form  between 
the  generalized  Cladose- 
lachian,  on  the  one  hand, 
and  the  Dipnoan  on  the 
other ;  or,  more  accu- 
rately, it  demonstrates 
that  the  stems  of  shark 
and  lung-fish  were  at  one 
time  drawn  very  closely 
together.  It  has  thus 
far  occurred  only  in  the 
Carbon  and  Permian, 
but  may  reasonably  be 
expected  in  lower  hori- 
zons as  a  contemporary 
of  the  earliest  lung- 
fishes. 

Pleuracanthus  is  in 
many  ways  the  most  in- 
teresting and  suggestive 
member  of  the  shark 
group ;  for  it  destroys 
many  of  our  conventional  ideas  as  to  the  general  characters 


84 


PLEURACANTHID   SHARKS 


Fig.    90  A.  —  Teeth    of    Pleuracanthus. 
(After  DAVIS.) 


XJ. 


essential  to  sharks.  That  it  was  actually  a  shark  cannot 
be  doubted ;  its  gills,  six  or  seven  in  number,  opened 
separately  to  the  surface ;  its  teeth  (Fig.  90  A)  were 
typically  shark-like,  arranged  in  many  rows  on  Meckelian 
and  palatoquadrate  cartilages ;  a  tuberculated  dorsal  spine 
was  present ;  claspers  occurred  in  the  male ;  the  vertebral 
column,  although  notochordal,  N,  presented  intercalary 

plates,  1C,  and  the 
jaw  was  essentially 
hyostylic,  HM.  On 
the  other  hand, 
many  of  its  struct- 
ures are  clearly  tran- 
sitional to  the  Dip- 
noan:  the  pelvic  fins 
are  shark-like,  with 
the  radial  supports, 
R,  arising  from  but 
one  side  of  the  line 
of  basals,  B ;  but  the 
pectoral  fin  is  typi- 
cally archipterygial, 
and  the  caudal  diphy- 
cercal,  as  in  the  lung- 
fishes.  In  this  re- 
gard the  continuous 
dorsal  fin,  with  its  separate  basals  and  radials,  B  and  R,  is 
again  noteworthy.  But  most  singular  of  all  the  features 
of  this  lung-fish-like  shark  were  its  integumentary  charac- 
ters ;  shagreen  tubercles  had  disappeared  on  the  body  sur- 
face, and  derm  bones  had  appeared  roofing  the  head :  their 
arrangement  (Fig.  90  B)  is  strikingly  similar  to  that  of  the 
lung-fish  of  Fig.  124. 


Fig.  90  B.  — Dermal  bones  of  the  head  roof  of 
Pleuracanthus.     X  5.     (After  DAVIS.) 


CHONDRENCHEL  YS  g  5 

The  final  form  of  Palaeozoic  shark  whose  structural  char- 
acters have  in  any  way  been  described  is  Chondrenchelys. 
It  appears  to  have  somewhat  resembled  the  Pleuracanthid 
in  its  elongate  form  and  tapering  tail ;  but  as  yet  the 
details  of  its  structure  have  not  been  discovered.  In  its 
vertebral  characters  it  had  certainly  made  a  marked  ad- 
vance ;  the  notochord  had  become  greatly  constricted ; 
and  well-marked  centra  and  arches  were  present.  These 
appear  to  have  been  highly  calcified,  and  show  a  peculiar 


Fig.  91.  —  Port  Jackson  shark,  Cestracion philippi  (?) .    X  ^.    (After  GARMAN.) 
Australia.    A.  Ventral.    B.  Anterior,  and  C.  Dorsal  aspect  of  head. 


beaded  or  fretted  structure  which  in  this  form  is  appar- 
ently unique. 

Other  ancient  sharks,  as  far  as  can  be  inferred  from 
fragmental  structures,  appear  to  have  closely  resembled 
forms  that  are  still  extant. 

Such  unquestionably  were  the  Cestracionts,  a  group 
of  sharks  especially  abundant  in  the  early  Palaeozoic 
seas,  judging  from  the  numbers  of  their  fin  spines  and 


36  PORT  JACKSON  SHARKS 

pavement  teeth  that  have  been  preserved.  Their  bygone 
role  was  certainly  a  long  and  important  one.  In  some 
of  their  forms  they  could  have  differed  but  little  from 
their  single  survivor,  the  Port  Jackson  shark,  Cestracion 
(Heterodontus)  (Fig.  91,  A,  B,  C).  In  others,  the  denti- 
tion and  dermal  defences  suggest  a  wide  range  in  evo- 
lution. Their  general  character  appears  to  have  been 
primitive,  but  in  structural  details  they  were  certainly 
specialized ;  thus  their  dentition  had  become  adapted  to  a 
shellfish  diet,  and  they  had  evolved  defensive  spines  at 
the  fin  margins,  sometimes  even  at  the  sides  of  the  head. 
In  some  cases  the  teeth  remain  as  primitive  shagreen 
cusps  on  the  rim  of  the  mouth,  but  become  heavy  and 
blunted  behind ;  in  other  forms  the  fusion  of  tooth  clus- 
ters may  present  the  widest  range  in  their  adaptations  for 
crushing ;  and  the  curves  and  twistings  of  the  tritoral  sur- 
faces may  have  resulted  in  the  most  specialized  forms  of 
dentition  (e.g.  Janassas,  Petalodonts,  Cochliodonts,  and  Psam- 
modonts  of  the  Coal  Measures)  which  are  known  to  occur 
not  merely  in  sharks  but  among  all  vertebrates.  Equally 
interesting  may  prove  the  evolutional  details  of  other 
cestraciont  structures  when  they  come  to  be  known. 
Ray-like  proportions  may  well  have  been  evolved  even 
among  the  earliest  Palaeozoic  forms. 

The  surviving  member  of  this  group,  Cestracion,  sug- 
gests in  itself  the  adaptations  of  a  bottom-living  form  in 
its  greatly  enlarged  pectorals.  Its  genus,  however,  has 
not  been  traced  earlier  than  the  Mesozoic,  although  its 
comparatively  generalized  dentition  (Fig.  27)  suggests  a 
far  more  remote  descent. 

It  is  of  interest  to  note  that  Cladoselache  approaches  in 
its  dentition  the  characters  of  the  primitive  Cestracionts 
(e.g.  Synechodus). 


88 


PRIMITIVE  LIVING  SHARKS 


Recent  Sharks 

The  forms  of  Sharks  and  Rays 
common  at  the  present  time  are 
generally  looked  upon  as  closely 
related  genetically,  although 
their  lineage  cannot  be  defi- 
nitely traced.  As  far  as  palae- 
ontological  evidence  goes,  they 
may  well  have  been  derived 
from  a  single  Palaeozoic  an- 
cestor. 

Perhaps  of  all  recent  forms, 
Chlamydoselache  (Fig.  92),  and 
Notidamis  (Heptanchus,  or  Hep- 
tabranchias)  (Fig.  93),  which  are 
universally  regarded  as  "primi- 
tive," have  inherited  most  di- 
rectly the  features  of  this  gen- 
eralized Palaeozoic  form.  But 
which  of  these  two  sharks  must 
be  regarded  as  resembling  its  re- 
mote ancestor  the  more  closely 
seems  to  the  writer  a  very  doubt- 
ful matter.  Chlamydoselache 
derives  its  great  interest  from 
its  late  discovery  (1884,  Gar- 
man),  rareness,  and  Pleuracan- 
thid  type  of  teeth  (Fig.  92,  A) ; 
but  now  that  it  has  been  taken 
in  numbers  —  comparatively  — 
in  deep  water,  one  is  inclined 
to  believe  that  many  of  its 


RECENT  SHARKS 


89 


"primitive"  features,  like  its  eel-like  shape,  may  partly  be 
due  to  its  environment :  its  resemblance,  moreover,  to  the 
Pleuracanth  has  since  been  found  to  be  of  a  superficial 
character.  Notidanus,  on  the  other  hand,  adds  to  its 
primitive  characters  the  presence  of  no  less  than  seven 


Fig.  94.  —  The  horned  dog-fish,  Squalus  acanthias,  L. 
in  U.  S.  F.  C.)     Atlantic. 


X  J.    (After  GOODE 


gill  slits,  —  a  feature  which  morphologists  generally  are 
inclined  to  regard  as  of  great  significance. 

The  many  forms  of  recent  sharks  have  certainly  not 
diverged  widely  from  the  stem  of  descent  which  Notidanus 
may  well  represent  :  they  retain  the  sub-cylindrical  body 
form,  specializing  more  or  less  to  environment;  in  deep- 
sea  genera  the  body  length  appears  proportionally  in- 


Fig.  95.  —  The  thrasher  shark,  Alopias  vulpes  (GmeL),  Bonap.    9.     X  TV.  Atlantic. 

creased  :  predatory  forms,  such  as  Squalus,  Alopias,  Lamna 
(Figs.  94,  95,  96),  acquire  great  size  and  strength,  travel 
great  distances,  and  are  enabled  to  become  cosmopolitan. 
Among  the  minor  details  to  which  their  evolution  has 
been  carried,  may  be  noted  :  the  pattern,  size,  and  arrange- 


9o 


RECENT  SHARKS 


ment  of  teeth  and  shagreen  denticles ;  the  calcification  of 
the  vertebrae  (great  differences  sometimes  occurring  in  the 
same  genus,  e.g.  Scyllium),  the  size,  disposition,  and  num- 


Fig.  96. — The  mackerel  shark,  Lamna  cornubica  (Gmel.),  Fleming.  X  sV. 
North  Atlantic. 

her  of  the  fins,  the  more  or  less  pouch-like  character  of 
the  sensory  canals. 

In  the  basking  shark,  Cetorhinus  (Selache)  (Fig.  96  A), 
widely  specialized  conditions  occur  in  the  gill  rakers, 
which  enable  the  throat  to  retain  the  smallest  food  organ- 


Fig.  96  A. —  The    basking  shark,    Cetorhinus  maximus,    (L.)    Blainville.      cf. 
X  sV.     (After  GOODE  in  U.  S.  F.  C.) 

isms.  In  another  shark,  Lcemargus  (Fig.  96  B\  the  eggs 
are  probably  fertilized  after  being  deposited,  —  a  condition 
unique  among  recent  Elasmobranchs. 


SQUATINA  AND  PRISTIS  gj 

The  different  families  of  the  existing  sharks  appear  to 
to  have  been  already  differentiated  during  the  early  Meso- 
zoic  times.  The  ancient  shark-like  form  had  then  given 
place  to  the  flattened  and  rostrated  types,  adapted  to  the 


Fig.  96  B.  —  The  Greenland  shark,  Lcemargus  borealis,  L.    X  &.    (After  G0NTHER.) 

conditions  of  bottom  living  and  to  the  special  character  of 
their  shell-fish  or  crustacean  diet. 

One  of  the  earliest  offshoots  from  the  main  selachian 
stem  appears  to  have  been  Squatina  (Fig.  97),  popularly 
known  as  the  monk-fish,  or  angel-fish.  As  early  as  the 
Mesozoic  times  it  was  existing,  differing  but  little  from  the 
recent  species.  Its  general  shape  is  shark-like,  although  its 


Fig.  97.  —  The    monk-,  or  angel-fish,  Rhlna  squatina.     ?.     X  &.    Atlantic, 
Mediterranean,  Pacific. 

head  and  trunk  are  clearly  depressed.  This,  together  with 
its  enlarged  pectoral  fins,  enables  it  to  take  a  position 
closer  to  the  bottom. 

The  recent  saw-fish,  Pristis  (Figs.  98,  98  A),  is  next  to 


02  SA  W-FISHES 

be  mentioned  as  a  form  somewhat  transitional  from  shark 
to  ray.  Its  body,  as  may  be  seen  in  the  figure,  has  been 
strikingly  flattened,  the  gill  openings  changing  their  posi- 
tion from  the  lateral  to  the  ventral  side,  but  the  fins  re- 
taining in  general  the  selachian  characters.  Its  singular 
rostrum  with  lateral  spike-like  teeth  is  unquestionably  a 


Fig.  98.  — The  saw-fish.     Pristis  pectinatus,  Latham.     ?. 
seas.     (After  GOODE  in  U.  S.  F.  C.) 


highly  specialized  organ.  Pristis  is  thus  far  known  not 
earlier  than  the  Eocene,  but  its  close  connection  genetically 
with  the  ancient  and  more  generalized  Pristiophorus  is 
usually  conceded. 

Pristiophorus  (Fig.  99)  is  certainly  more  closely  allied 
to  the  sharks :  its  gill  slits  have  not  as  yet  acquired  their 
ventral  position,  and  its  rostrum  suggests  the  ancestral 


Fig.  98  A.  —  Saw-fish,  ventral  view. 

conditions  of  that  of  Pristis.  Its  barbel-like  structures, 
however,  distinguish  this  form  clearly  from  all  other 
Elasmobranchs.  It  is  known  to  have  occurred  as  early 
as  the  Jura. 

The  Skates  or  Rays  are  well  known  to  represent  the 
most  highly  modified  survivors  of  the  ancient  stem  of  the 


SKA  TES 


93 


sharks ;  they  appear  comparatively  late  in  time,  and  may 
well  be  regarded  as  the  culminating  forms  of  the  specializ- 
ing bottom-living  sharks  of  the  Mesozoic.  Whether  they 
are  directly  descended  from  forms  like  Squatina  or  Pristio- 


Fig.  99. —  Pristiophorus  (cirratus). 


(After  JAEKEL.)     Australia. 


phorus  must  be  looked  upon  as  exceedingly  doubtful,  as 
the  depressed  body  form  may  possibly  have  arisen 
independently  in  these  different  families.  The  most 
nearly  ancestral  form  of  the  skates  appears  to  have  sur- 
survived  in  Rhinobatus  (Fig.  100).  The  shark-like  body 
form  is  here  most  nearly  retained,  and  its  fin  structures 


Fig.  loo.  —  Rhinobatus  planiceps.     ?,.     X  }.     (After  CARMAN.)     (The  lower 
portion  of  the  figure  showing  ventral  side.)     S.  Spiracle.     GO.  Gill  slits. 

are  the  least  specialized ;  these  transitional  characters  of 
Rhinobatus  become  more  prominent  in  view  of  its  ancient 
occurrence :  its  genus  was  clearly  defined  as  early  as  the 
Oolite. 


94 


FLATTENED   SHARKS 


The  body  form  of  the  Skate  (Fig.  101)  has  become 
admirably  adapted  to  bottom  living;  it  is  exceedingly 
flattened  anteriorly,  its  head  and  trunk  and  paired  fins 
fusing  so  perfectly  that  from  the  surface  view  one  could 
not  define  their  limits  ;  the  tail  region,  on  the  other  hand, 
has  dwindled  away  to  rod-like  or  whip-like  proportions. 


Fig.  ioi.—  The  barn-door  skate,  Raja  Icevis,  Mitch, 
in  U.  S.  F.  C.) 


1.     x  J.     (After  GOODE 


In  the  process  of  flattening,  the  gill  openings  take  their 
appearance  early  in  the  ventral  side  of  the  body,  and  the 
pectoral  fins,  enlarging  rapidly,  press  closely  forward  at 
the  side  of  the  flattened  head,  fusing  with  its  tissues. 
Motion  is  now  accomplished  by  the  gentle  undulation 
of  the  long  horizontal  fin  margin  :  and  the  enlarged 


AFFINITIES   OF   THE  ELASMOBRANCHS 


95 


anterior  element  of  the  fin  stem,  by  being  raised  or  de- 

pressed, comes  to  direct  the  upward  or  downward  motion 

of  the  fish.     In  this  mode  of  movement  seems  to  have 

been  paralleled  the  undulation  of  the  ancestral  fin  fold. 

On  the  fish's  dorsal  side  colour  adaptations  have  become 

marked,    the    ventral 

aspect   becoming  de- 

ficient or  wanting  in 

pigment.    In  its  hab- 

its the  skate  mimics 

the     colour    of     the 

bottom    and    glides 

along    inconspicuous- 

ly,   apparently   with- 

out movement  ;  when 

alarmed,  it  will  press 

its  enlarged  and  flat- 

tened fins  so  closely 

to  the  bottom  that  it 

appears     to     adhere, 

and  is  to  be  dislodged 

only   with  the  great- 

est efforts. 

Two   of   the   aber- 

rant forms  Of  rays  are 

shown    in    Figs.     102 

and  1  02  A.     The  for- 

mer, the  Torpedo,  is  remarkable  on  account  of  its  electric 

organs  ;  the  latter,  Dicerobatis,    on    account    of  the  great 

breadth  of  its  pectorals,  and  its  enormous  size. 


pig.  102.  —  The  torpedo,    Torpedo  occidcnta- 

*•    x  *•    (After  GOODE  in  u.  S. 


96  KINSHIPS   OF  SHARKS 

Affinities 

In  concluding  the  present  chapter,  the  probable  affini- 
ties and  interrelationships  of  the  Elasmobranchs  may  be 
summarized  as  follows  (v.  Fig.  103) :  — 

1.  Of  all  known  stems  that  of  the  shark  is  most  nearly 
ancestral  in  the  line  of  jaw-bearing  vertebrates. 

2.  A  generalized  form  not  unlike  Cladoselache  might 
well  represent  the  ancestor  of  Pleuracanthid,  as  well  as 
of  the  primitive  Cestraciont,  of  Acanthodes,  and  of  the 
modern  sharks  and  rays. 


Fig.  102  A.  —  The  mantis,  or  devil  ray,  Cephaloptera  (Dicerobatis)  d 
(After  GUNTHER.)     Tropical  seas. 


raco. 


3.  On    the   evidence    of    the    Permian   Pleuracanthids, 
lung-fishes    (Dipnoans)    and     the     earliest     bony     fishes 
(Crossopterygians)  are  to  be  derived  from  an  advancing 
shark  type. 

4.  From    the    ancestral    stem    of    the    recent    sharks 
Cestracionts  were  the  most  early  differentiated  :  it  is  one 
of  their  more  generalized  forms,  Cestracion,  that  has  alone 


KINSHIPS   OF  SHARKS  ^ 

survived  among  the  widely  evolved  genera  and  families  of 
Palaeozoic  times. 

5.  The  more  primitive  types  of  modern  sharks,  Chlamy- 
doselache,  Notidanus,  represent  in  an  almost  differentiated 
condition  the  Palaeozoic  phylum. 

6.  The  modern  rays  are  derived  in  early  Mesozoic  times 
from  the   main  shark  stem,   not  (in  the  opinion    of   the 
writer)  descended  from  Cestracionts,  Pristids,  Pristiopho- 
rids,  or  even  (?)  Rhinids. 

7.  Chimaeroids,  next  to  be  discussed,  represent  the  most 
ancient  of  known  offshoots  from  the  (Pre-Silurian  ?)  sharks  : 
they  are  not  degenerate  in  their  essential  structures,  nor 
are  they  connected  with  the  ancestral  phylum  of  the  lung- 
fishes,  save  through  a  common  descent  from  early  shark- 
like  ancestors. 

These  results  the  writer  has  expressed  in  the  diagram 
on  the  following  page.  The  diverging  phyla  are  indicated 
as  they  are  represented  historically ;  their  primitive  con- 
currence with  the  main  line  of  descent  is  suggested  by 
dotted  lines. 


Ancestral  Elasmobranch. 


(TABLE  III) 


Cladoselache. 

thodian. 

-     Pleuracanthid. 


CXENO- 
ZOIC. 


Fig.  103.  —  Scheme  suggesting  the  interrelationships  of  Sharks,  Chimaeroids, 
and  Lung-fishes. 

98 


THE   CHI1VLEROIDS 

CHIM^ROIDS  are  shark-like  in  their  general  characters, 
but  cannot  be  looked  upon  as  in  any  strict  sense  closely 
associated  with  the  Elasmobranchs.  They  constitute  the 
second  of  the  more  important  groups  of  fishes.  Their 
typical  representative  is  the  Chimaera,  spook-fish,  or  sea- 
cat  (Fig.  119). 

Structural  Characters 

The  typical  structures  of  Chimaera  are  shown  in  the  dis- 
section given  in  Fig.  104.  Its  thick,  round,  and  blunted 
head  tapers  away  gradually  to  the  tip  of  a  diphycercal  tail, 
C.  The  body  surface  is  generally  smooth.  The  paired  fins 
are  somewhat  shark-like,  but  their  dermal  margins  have  be- 
come greatly  enlarged,  tapering  distally  to  an  acute  point ; 
the  foremost  dorsal  fin  provided  with  an  anterior  spine  folds 
like  a  fan  and  may  be  depressed  into  a  sheath,  SH,  in  the 
body  wall ;  this  fin  and  the  hinder  ones  are  largely  dermal, 
D',  basal  and  radial  supports  existing  only  at  B\  R'.  The 
gill  arches,  BA,  may  be  seen  to  be  closely  drawn  together; 
their  outer  openings  are  now  reduced  to  the  slit-like  aper- 
ture beneath  the  dermal  flap,  OP.  Teeth  exist  in  the 
form  of  dental  plates,  closely  fused  with  the  jaws  ;  as 
shown  in  the  figure,  D,  three  of  these  occur  in  each  side, 
a  single  one  on  the  mandible,  an  anterior  and  posterior  on 

99 


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v«  o    O.  o  "* 

A 


100 


STRUCTURES   OF  CHIM&ROIDS  IOi 

the  upper  jaw  (" premaxillary  "  and  "palatine") ;  they  are 
studded  with  hardened  points,  or  "tritors"  (Figs.  109-112). 
The  sense  organs  are  similar  to  those  of  sharks  ;  the  nasal 
capsule,  NAS,  has  both  an  anterior  and  a  posterior*  open- 
ing,  O,  O',  the  latter  within  the  cavity  of  the  mouth. 

The  visceral  parts  are  decidedly  shark^ike^fte!  3ige** 
tive  tube  is  straight  (p.  263)  ;  the  intestine,  /,  with  a  spiral 
valve  of  three  turns  ;  the  liver,  L,  is  prominent ;  the 
kidney,  K,  reproductive  organs,  T,  and  their  ducts,  VD, 
SSy  VS,  and  abdominal  pores  are  as  in  sharks ;  the  intes- 
tine, however,  opens  directly  to  the  surface,  A,  separating 
an  anal  from  a  urogenital  aperture,  UG.  The  mesenteries 
are  string-like. 

The  male  fish  is  provided  with  a  highly  specialized  intro- 
mittent  organ,  CL ;  it  has  a  supplemental  clasping  organ, 
VC,  at  the  front  margin  of  each  ventral  fin,  V  (cf.  also  Fig. 
116  and  Fig.  ii6#),  and  a  retractile  spine  in  the  region  of 
the  forehead,  MSP  (cf.  Figs.  113  and  115). 

The  skeleton  of  a  Chimaeroid  is  shown  in  the  following 
figure  (Fig.  105).  Its  structure  is  cartilaginous.  The  ver- 
tebral axis  is  notochordal ;  its  sheath,  lacking  in  definite 
centra,  is  strengthened  anteriorly  by  a  series  of  calcified 
rings.  In  the  anterior  region  of  the  trunk,  neural  proc- 
esses, interneurals,  and  neural  spines,  NP,  IN,  NS,  to- 
gether with  haemal  processes,  occur  as  in  sharks ;  toward 
the  tail  region  they  fade  away,  and  before  joining  with 
the  head  at  the  occipital  condyles,  OC,  they  fuse  into  a 
compact  mass,  joining  with  the  basal  supports  of  the 
dorsal  fin. 

The  cranium  is  of  a  highly  compacted  structure;  its 
vertical  height  has  been  greatly  produced ;  the  orbits,  OR, 
are  of  great  size  and  are  separated  from  each  other  by  a 
membranous  septum.  The  snout  region  is  greatly  meta- 


ifl 


*  sea  3-^5  s- 

.a  a<u-a£Ot;  =  ? 
a  g-«g*     £•§>£ 

*^        !/)•«-•      r-»*w.          -^^CC-^ 


i 


^5  oO  a 


102 


STRUCTURES   OF  CHIMJZROIDS     ,  IO^ 

morphosed ;  the  mandible  appears  to  be  autostylic,  or  artic- 
ulated directly  with  the  skull  cartilage,  PQ.  The  gill 
arches  are  shark-like,  b\  '"he  hyoid  arch  appears  far  less 
modified  than  in  sharks  ;  its  upper  element,  HM,  is  thus 
unconnected  with  either  th:  skull  or  the  joint  of  the  jaw; 
its  distal  element,  CH,  has,  however,  developed  a  series  of 
specialized  supports  for  the  dermal  gill  shield,  OP.  The 
study  of  the  fin  supports  shows  the  dorsal  elements,  B  +  R, 
representing  probably  the  radial  and  basal  elements  to- 
gether, arranged  in  a  single  row  margined  distally  by  the 
longitudinal  ligament,  LL,  supporting  the  dermal  func- 
tional fin,  D.  The  paired  fins  are  readily  reduced  to  the 
plan  of  those  of  Fig.  84;  their  girdles,  however,  seem  to 
have  acquired  more  modified  characters,  their  ventral  and 
dorsal  elements  greatly  increasing  in  size. 

Chimasroids  as  a  group  have  received  but  a  small  share 
of  the  attention  paid  to  the  other  fishes  ;  their  living 
forms  are  few  and  comparatively  rare ;  their  embryology 
and  larval  history  are  unknown  ;  and  their  life  habits  have 
been  suggested  only  in  the  work  of  Dr.  Giinther  (Chal- 
lenger Report).  His  record  of  the  taking  of  immature 
specimens  of  Chimara  at  great  depths  seems  thus  far  the 
most  important  clue  as  to  the  conditions  of  their  living 
and  breeding.* 

Fossil  Chimaroids 

Fossil  Chimaeroids  have  left  behind  them  very  imperfect 
records  of  the  history  of  their  group.  Like  the  sharks, 
little  more  than  their  dental  plates  and  fin  spines  have 
usually  been  preserved.  The  structures  of  some  of  their 
ancient  members  appear  to  have  differed  little  from  those 
just  described  in  the  recent  Chimaera.  In  Ischyodust 

*  Cf.  also  Goode  and  Bean,  on  Harriott^  P.  U.  S.  Nat.  Mus.,  XVII.  471-473. 


FOSSIL    CHIMsEROIDS 

a  Jurassic  form  (Fig.  105  A),  the  skeletal  structures  are 
readily  comparable  to  those  of  Fig.  105.  In  the  case  of 
two  of  the  Mesozoic  genera,  however,  the  evolution  of 
the  Chimaeroids  had  evidently  attained  a  high  degree 
of  specialization :  Myriacanthus  and  Squaloraja,  whose  par- 
tial restoration  has  been  attempted  in  Figs.  106  and 
io6A,  must  be  both  looked  upon  as  highly  modified  forms ; 
their  snouts  and  frontal  spines  are  greatly  enlarged,  and 
their  dental  plates  (Figs.  107  and  108)  widely  divergent 
from  the  general  Chimaeroid  type :  in  Myriacanthus  a  series 
of  membrane  bones  occurs  in  the  head  region  (Fig.  106, 
B,  C).  In  Squaloraja  a  horizontally  flattened  body  shape 
parallels  the  development  of  the  ray-like  form  of  sharks. 


Fig.  105  A.  —  The  Mesozoic  Chimaeroid  hchyodus.     X  |.     (After  ZlTTEL.) 

Living  Chimceroids 

The  Chimaeroids  of  to-day  must  be  looked  upon  as  the 
survivors  of  a  group  comparatively  numerous  in  Mesozoic 
times :  the  few  existing  forms  accordingly,  from  the  palae- 
ontological  standpoint,  acquire  an  exceptional  interest. 
They  have  been  grouped  under  three  genera,  —  Harriotta, 
Callorhynchns,  and  Chimara.  The  first  of  these  (Fig. 
117,  A,  B,  C)  has  been  only  recently  discovered,  and  but 
a  few  examples  have  been  taken  ;  it  merits  especial  atten- 
tion, since  it  is  unquestionably  the  most  shark-like  of 
known  Chimaeroids.  In  the  male  it  lacks  entirely  the 
frontal  spine  and  has  its  claspers  in  an  exceedingly  un- 


FOSSIL    CHIM&ROIDS 


105 


X  "o 


differentiated  condition.     The  eggs  are  evidently  fertilized 
after  they  have  been  extruded. 

The  second  genus,  Callorhynchus,  is  represented  by  but 


"|t|! 

*  £  S  £  f 


106 


FIG.  113 


MC 


114 


^^^^ 


116 


sc  v 

Figs.  113-116  A.  —  Spines  and  clasping  organs  of  Chimaeroids.  113.  Clasping  spine 
of  the  forehead  of  male  Chimcera  colliei.  X  6.  114.  Myriacanthus  dorsal  spine.  (After 
L.  AGASSIZ.)  115.  Frontal  spine  of  male  Squaloraja.  (From  SMITH  WOODWARD.) 
116.  Ventral  fin  and  clasping  organs  of  male  Chimcera  colliei.  X  i.  116  A.  View  of  tip 
of  hinder  clasper  (intromittent  organ),  when  the  three  tips  are  drawn  together. 

A.  Anus.  A  V,  Anterior  rim  of  ventral  fin,  specialized  as  a  clasping  organ.  BC.  Body 
of  the  posterior  clasper  (intromittent  organ).  D.  Dermal  denticles.  DS.  Dermal  spine- 
like  denticles.  D  T.  Dermal  tubercles.  GD.  Urinogenital  aperture.  J.  Jointed  base  of 
inner  ventral  element  of  intromittent  organ.  MC,  Mucous  canal.  S.  Sheath  of  frontal 
spine.  SC.  Sperm  groove  of  inner  face  of  clasper.  V.  Ventral  fin. 

107 


i  I' 


Fig.  117.  —  Harriotta  raleighana,  Goode  and  Bean.  tf.  X  \.  Anew  genus 
of  Chimasroid  —  a  bathybial  form.  A.  Ventral  view,  showing  rudimentary  claspers. 
B,  C.  Immature  specimens. 

108 


CALL  ORHYNCHUS 


a  single  species,  C.  antarcticus.  It  is  said  to  be  common  in 
the  Straits  of  Magellan,  and  is  popularly  known  as  the 
Bottle-nosed  Chimaera  (Fig.  118,  A,  B).  Its  remarkable 
snout  is  well  supplied  with  sense  organs,  and  its  pad-like 
dilation  in  front  of  the  mouth  is  evidently  of  barbel-like 
function ;  it  illustrates  closely,  no  doubt,  the  remarkable 
snout  process  of  Myriacanthus.  Callorhynchus  is  shark- 
like  in  its  general  shape;  and  its  caudal,  dorsal  and  ventral 


Fig.  118.  —  The  bottle-nose  Chimaera,  Callorhynchus  antarcticus,  ?.  X  &.  From 
Magellan  Straits.    A.  Dorsal  aspect.    B.  Ventral  view  of  head.    (After  GARMAN.) 

fins  correspond  closely  in  appearance  and  structure  with 
those  of  certain  sharks ;  the  greatly  enlarged  pectoral  fins 
have,  however,  a  more  highly  specialized  character ;  they 
stand  boldly  out  from  the  sides  of  the  body,  and  their 
bases  are  rounded  and  muscular.  The  mucous  canals 
(Garman)  have  paralleled  the  saccular  or  tubular  struct- 
ures of  the  majority  of  sharks.  The  mandible  (Fig.  no) 
shows  but  a  single  broad  tritoral  area. 


110 


RECENT   CHIM&ROIDS 


Chimaera,  the  third  genus  of  the  recent  forms,  is  well 
represented  in  the  commoner  form,  C.  monstrosa  (Fig.  1 19, 
A,  B).  This  species  is  widely  distributed  in  the  Mediter- 
ranean and  Atlantic,  taken  usually  in  deep  water;  it  is  the 
largest  of  the  living  species,  often  attaining  a  yard  in 
length.  Its  occurrence  is  usually  erratic :  in  a  favourable 
locality,  as  at  Messina,  months  often  elapse  before  one  is 
taken  ;  at  other  times  many  will  be  brought  in  in  the 
course  of  a  few  days.  The  Portuguese  species,  C.  affinis, 


Fig.  119. — The  sea-cat,  Chimcera  monstrosa, 
snout.     B.  Front  view  of  head.     (After  GARMAN.) 


X  5.    A.  Ventral   view  of 


is  said  to  be  numerous  in  the  deep  fishing  grounds ;  the 
writer  has  seen  it  in  the  Lisbon  market,  where  from  its 
low  price  it  evidently  ranks  with  the  sharks  as  a  food  fish. 
The  smaller  Pacific  C.  colliei  (Fig.  104),  rarely  half  a  yard 
in  length,  differs  sharply  from  the  other  species,  and  is 
therefore  often  given  rank  as  a  distinct  genus,  Hydro- 
lagus,  Gill.  The  writer  learns  from  his  friend  Dr.  Bean 


AFFINITIES   OF  CHIM&ROIDS  IIZ 

that  it  occurs  abundantly  in  the  shallow  waters  of  Van- 
couver ;  it  is  there  well  known  as  the  "rat  fish,"  and  may 
often  be  seen  in  the  neighbourhood  of  the  docks,  swim- 
ming slowly  at  the  surface. 

The  shape  of  the  body  of  Chimaera  seems  in  some  re- 
gards to  have  diverged  from  the  more  shark-like  form  of 
Callorhynchus.  Its  organs  have  become  concentrated  in 
the  pectoral  region,  and  the  disturbance  in  the  curve 
normals  of  the  fish  seems  to  have  caused  the  shortening  of 
the  snout,  and  the  sudden  dwindling  of  the  hinder  trunk 
region;  the  tail,  with  its  thread-like  terminal,  the  opis- 
thure  (Fig.  120),  is  accordingly  to  be  looked  upon  as  de- 


Fig.  I2O. —  Chimcera  monstrosa,  tf.  Juv.  X  about  §.  (After  L.  AGASSIZ.) 
The  anterior  ventral  clasper  is  noted  at  X;  the  tail  terminates  in  a  thread-like 
opisthure. 

generate.  In  the  anterior  region,  however,  a  number  of 
what  seem  to  be  primitive  characters  have  been  retained ; 
the  mucous  canals  are  groove-like ;  and  the  dental  plates 
(Figs.  109,  109^)  exhibit  a  series  of  tritoral  areas. 

Affinities 

All  that  is  known  of  Chimaeroids,  living  or  fossil,  gives 
but  little  definite  knowledge  of  the  kinships  or  evolution 
of  the  group.  Their  shark-like  structures  cannot  be  shown 
to  have  taken  their  origin  from  shark-like  conditions. 
Thus  the  dental  plates  even  of  the  most  ancient  forms 
do  not  suggest  their  derivation  from  shagreen  cusps ;  the 


!  j  2  CHIM^R  OIDS 

beak-like  jaws  of  the  Devonian  Rhynchodus  (Fig.  in), 
of  the  Devonian  Ptyctodus,  or  of  the  Mesozoic  genera, 
e.g.  Ischyodus  (Fig.  112),  differ  little  in  their  structures 
from  those  of  their  living  kindred  (Figs.  109,  109  A,  1 10). 
The  tritors  accordingly  are  only  doubtfully  to  be  derived 
from  the  fusion  of  the  primitive  basal  substance  of  the  teeth 
with  the  tissue  of  the  jaws.  But  the  history  of  Chimae- 
roids  tells  of  their  ancient  importance  and  of  the  diversity 
of  their  forms,  and  demonstrates  that  they  cannot  be  con- 
nected with  other  existing  forms  of  fishes.  In  Liassic 
times  their  specialized  members  bore  the  same  relation  to 
Chimaera  as  did  the  aberrant  Cestracionts  of  the  Coal 
Measures  to  the  simpler  sharks.  In  their  dental  evolution 
they  had  even  reached  a  more  specialized  condition  than 
the  Cochliodonts  (Cestracionts  ?).  Thus  in  Myriacanthus 
and  Squaloraja,  "all  anterior  prehensile  teeth  have  disap- 
peared, and  the  growth  of  the  dental  plates,  instead  of 
taking  place  exclusively  at  the  inner  border,  seems  to  have 
gradually  extended  to  the  whole  of  the  attached  surface. 
The  Chimaeridae  exhibit  an  advance  in  the  circumstance 
that  all  the  dental  plates  are  thickened,  while  the  hinder 
upper  pair  are  both  closely  apposed  in  the  median  line  and 
much  extended  backward  "  (Smith  Woodward).*  Squaloraja 
had  certainly  attained  a  high  degree  of  evolution  in  the 
calcified  vertebral  rings,  and  in  its  specialized  girdles,  fins, 
and  clasping  organs.  Myriacanthus,  on  the  other  hand, 
while  retaining  its  ancient  vertebral  characters,  had  evolved 
a  well-marked  series  of  membrane  bones. 

One  cannot  deny  that  the  study  of  Chimseroids  as  a 
group  emphasizes  many  of  their  structural  affinities  to 
the  sharks.  They  resemble  them  in  their  cartilaginous 
skeleton,  fins  and  girdles,  "  claspers,"  integument,  and 

*  Cat.  Fossil  Fishes  II,  xvi. 


KINSHIPS   OF  CHIM^.ROIDS  U^ 

sense  organs :  they  present  similar  visceral  characters, 
spiral  intestine,  heart,  gills,  abdominal  pores,  renal  and 
reproductive  organs. 

Their   more    important    divergences    from  the   plan    of 
elasmobranchian  structure  may  thus  be  summarized :  — 

I.  SKULL  AND  MANDIBLE  (v.  pp.  252,  256).     The  mandi- 
ble articulates  directly  with  what  appears  to  be  the  carti- 
lage of  the  cranium,  i.e.  without  the  hyoid-arch  element 
serving  as  the  suspensorium  (Autostylic,  p.  257). 

II.  FINS,  paired  (Wiedersheim)  and  unpaired   (Ryder), 
and  fin  defences.     The  first  dorsal,  armed  with  an  anterior 
spine,  is  so  specialized  that  it  folds  like  a  fan,  and  may  be 
depressed  into  a  receptive   sheath.     The  tail  is   (second- 
arily) diphycercaL 

III.  SKIN  DEFENCES  AND  TEETH.     Shagreen  tubercles 
occur  in   Chimaeroids   and   are   in    every  way  shark-like. 
They  are  scattered  thickly  over  the  entire  dorsal  region 
in  Menaspis*  sparsely  in  Squaloraja.     They  occur  in  the 
head  region  and  on  the  spines  in  Myriacanthus  (Figs.  106 
C,  1 14)  ;  and  on  the  head,  spine,  and  clasper  tips  of  recent 
forms  (Figs.  113  D,  116  D).     But  dermal  bones  also  occur, 
as  in  Myriacanthus  (Fig.  106  B),  which  do  not  outwardly 
resemble  the  structures  of  ancient  sharks  shown,  e.g.  in 
Fig.  90  B.     The  dermal  plates  protecting  the  suborbital 
sensory  canal  of  Chimaera  (Fig.  104,  DP)  must  be  looked 
upon  as  specialized  defences,  not  as  degenerate  remnants 
of  a  complete  dermal  armouring  (Pollard).     And  the  dental 
plates,  as  already  noted  (p.  99),  are  altogether  unshark-like ; 
their  tritors  are  few  in  number  and  constant  in  position, 
suggesting  an  origin  from  more  superficial  tooth  centres, 
but  these  in  turn,  like  the  toothplates  of  Cestracionts,  may 
have  been  evolved  from  shagreen  denticles. 

*  Jaekel,  SB.  d.  Gesell.  nat.  Freunde,  Berlin,  1891,  Nr.  7. 

I 


U4 


CHIMAEROIDS 


IV.  GILL    ARCHES.     The   gills     have    become     drawn 
closely  together  as  in  the  more  highly  evolved  types    of 
fishes  (e.g.  bony  fishes),  and  are  enclosed  by  a  protective 
dermal  flap  which  fringes  the  sides  of  the  head.     The  con- 
centration of  the  arches  and  the  appearance  of  the  dermal 
shield  suggest,  however,  the  conditions  we  have  seen  in 
ancient  sharks  (Cladoselache,  Chlamydoselache,  Acantho- 
des),  and  cannot  be   given   significance  as  the   ancestral 
form  of   the  opercular   apparatus    of   Teleostome.     Even 
the   similar  conditions    of   the    Chimaeroid    and    ancient 
shark  may  well  have  been  evolved  independently.     It  is 
interesting  to  note   that    in    Chimaeroids   the   spiracle   is 
absent. 

V.  BRAIN.     The   brain  structure  is  archaic.     Its  gen- 
eral  plan    is,   however,    more  'shark-like    than    Dipnoan 
(Wilder,  Ref.  p.  244). 

VI.  LATERAL  LINE.     The  sensory  canals  possess  many 
distinctive  features ;  they  retain  their  groove-like  charac- 
ter, but  become  widely  sacculated  and  dilated,  especially 
in  the  snout  region. 

VII.  CLASPING   SPINE.     The  forehead   clasper   of    the 
male    has  been  a  well-marked    character   of   Chimaeroids 
from  Liassic  time.     It  folds  anteriorly  into   a  receptive 
groove ;    its    distal    end,    studded    with    recurved    spines, 
serves  in  the  recent  forms    for   strongest    retention.     It 
seems  to  represent  morphologically  the  anterior  spine  of 
a  dorsal  fin  (cf.  Pleuracanthus,  p.  83). 

In  spite  of  these  differences,  however,  the  kinships  of 
the  Chimaeroids  seem  unquestionably  nearer  the  stem  of 
the  sharks  than  that  of  other  fishes.  On  existing  evi- 
dence the  Chimaeroid  could  not  have  been  derived  from 
either  Teleostome  or  lung-fish ;  nor,  on  the  other  hand, 
could  any  of  the  larger  groups  of  fishes  be  reasonably 


AFFINITIES   OF  CHIM&ROIDS  r  !  5 

derived  from  its  conditions  as  ancestral.  The  dentition 
of  Chimaeroids  alone  is  so  remarkable  that  no  direct  proc- 
ess of  differentiation  could  convert  it  into  the  structures  of 
lung-fish  or  Ganoid.  A  number  of  archaic  features  draw 
fishes  together  in  the  lines  of  their  descent,  but  they  can- 
not be  interpreted  as  linking  the  Chimaeroids  with  the 
Dipnoans,  or  the  Dipnoans  with  the  Chimaeroids.  Auto- 
stylism,  often  adduced  to  ally  these  groups,  differs  widely 
in  its  characters  in  each  (p.  254)  :  and  the  apparent  similar- 
ities in  dental  plates  and  membrane  bones  are  closely 
paralleled  by  the  sharks.  The  diphycercal  tail  of  the 
Chimaeroid  can  be  made  no  standard  of  comparison,  since 
it  is  evidently  a  secondary  structure,  arising  within  the 
limits  of  the  group,  as  it  may  well  have  done  among 
sharks  (Pleuracanthus)  or  Teleostomes  (Polypterus,  eel). 

If  the  sum  of  the  general  characters  of  Chimaeroids  be 
considered,  their  affinities  would  clearly  be  to  the  most 
ancient  sharks.  Their  structures  are  not  so  widely  at  vari- 
ance with  those  of  Elasmobranchs  that  they  cannot  rea- 
sonably be  derived  from  their  more  generalized  conditions 
in  vertebral  characters,  cranium,  mandible,  girdles,  fins, 
membrane  bones,  gills.  Absence  of  swim-bladder  is  again 
strikingly  shark-like.  Like  the  ancient  sharks,  they  have 
been  well  adapted  for  survival  by  evolving  but  few  special- 
ized structures  (e.g.  dentition,  gills).  Their  ventral  clasp- 
ing organs  separate  them  clearly  from  the  Dipnoans. 
Until  the  discovery  of  Harriotta  the  frontal  clasping  spine 
remained  as  one  of  the  most  distinctive  features  of  Chi- 
maeroids ;  its  high  degree  of  specialization  in  Liassic  times 
is  alone  significant  of  the  antiquity  of  their  descent. 


VI 

• 

THE    LUNG-FISHES 

LUNG-FISHES,  or  Dipnoans,  have  long  been  looked  upon 
as  the  linking  type  between  amphibians  and  fishes.  In 
some  regards  of  structure  they  approach  the  primitive 
sharks  ;  in  others,  they  resemble  so  closely  the  salamanders 
that  they  were  recently  regarded  by  W.  N.  Parker  as  worthy 
of  a  class  by  themselves,  intermediate  between  fishes  and 
amphibians.  As  with  the  Chimaeroids,  their  few  surviving 
members  give  but  a  mere  suggestion  of  the  former  size 
and  importance  of  the  group. 

Structural  Characters 

The  general  structural  plan  of  a  Dipnoan  is  shown  in 
the  adjoining  figure  (Fig.  121),  taken  from  a  dissection  of 
the  African  form,  Protopterus.  Its  thick,  spindle-shaped 
body,  enclosed  in  rounded,  horn-like  scales,  CS,  terminates 
in  a  diphycercal  tail,  CF.  The  head  is  salamander-like 
both  in  shape  and  in  slimy  integument.  The  paired  fins 
(schematized  in  the  figure,  PF,  VF)  are  archipterygial. 

The  head  region  is  characterized  by  a  cartilaginous  brain 
case,  roofed  by  dermal  bones,  HR\  a  mandible,  MA, 
directly  articulated  with  the  skull  (autostylic) ;  an  anterior 
and  posterior  nares,  NO,  —  the  former  opening  under  the 
lip,  the  latter  within  the  mouth  ;  a  row  of  small,  compressed 
(unsegmented)  gill  arches,  GA,  whose  single  outer  aperture 

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is  guarded  by  an  operculum,  OP.  The  stunted  external 
gills  which  here  protude,  EB,  are  sometimes  looked  upon 
as  significant  of  an  ancestral  condition  (Garman,  Wieders- 
heim). 

The  viscera  are  somewhat  shark-like  in  their  features. 
They  include  a  short  digestive  tract,  with  well-marked 
spiral  intestinal  valve,  SIV\  a  fenestrated  dorsal  mesen- 
tery, DM\  a  large,  elongate  liver,  L\  a  heart  whose 
arterial  cone,  CA,  contains  transverse  rows  of  valves  ;  a 
cloaca,  abdominal  pores  (or  pore),  A ;  and  a  rectal  caecum, 
CC  (v.  p.  263).  The  elongate  kidney,  K,  the  ovary,  O  Vy 
with  its  many  small  eggs,  and  the  long,  paired,  sacculated 
air-bladder  (lung)  may  be  named  as  among  the  least  shark- 
like  of  its  visceral  characters. 

The  skeleton  of  a  Dipnoan  (Fig.  122)  is  almost  entirely 
cartilaginous.  A  stout  notochord,  encased  in  a  heavy 
sheath,  NCH,  passes  from  the  skull  to  the  tip  of  the  tail : 
vertebral  centra  encroach  upon  it  only  in  the  caudal  region, 
C.  Dorsal  and  ventral  processes,  arranged  in  metameral 
sequence,  extend  from  the  notochordal  sheath  outward  and 
become  distally  the  cartilaginous  supports  of  the  dermal 
unpaired  fin.  The  proximal  elements  might  thus  be  re- 
garded as  neural,  N,  NS,  or  haemal  processes  and  spines, 
the  distal  elements  as  equivalent  to  the  basal  and  radial  fin 
supports,  B  +  R.  A  stout,  longitudinal  ligament,  LL, 
serves  to  connect  the  outer  ends  of  the  cartilaginous 
processes,  as  well  as  the  proximal  ends  of  the  dermal  fin 
rays.  The  ribs  are  probably  the  homologues  of  the  haemal 
processes  ;  the  most  anterior  pair,  greatly  enlarged,  extends 
downward  on  either  side  as  the  occipital  ribs,  OR,  special- 
ized in  the  function  of  the  air-bladder. 

The  structure  of  the  paired  fin  is  normally  of  the 
archipterygial  form  of  Fig.  54.  In  Protopterus,  however, 


120 


LUNG-FISHES 


(Fig.  122),  this  plan  of  structure  is  somewhat  obscured  by 
the  rudimentary  character  of  the  radial  and  basal  elements, 
R  4-  D,  although  the  fin  stem  presents  a  well-marked 
jointed  character,  B.  The  pelvic  girdle,  a  solid  plate  of 
cartilage,  is  produced  anteriorly  into  a  narrow  median  out- 
growth, PG,  and  laterally  into  a  pair  of  dorsal  spurs,  PG'. 
The  shoulder  girdle  is  composed  on  either  side  of  a  large 
ventral  element,  SG,  which  meets  its  fellow  in  the  median 
ventral  line,  and  of  a  short  dorsal  element,  SG',  which 
connects  it  with  the  skull. 


Fig.  122  A.  —  Jaws  and  skull  of  Protopterus  annectans,  figured  in  front  and  side 
aspects,  showing  paired  dental  plates,     x  i.     (After  NEWBERRY.) 

M.  Dental  plates  of  (dentary)  mandible;   P.  of  palatopterygoid ;    V.  of  vomer. 


In  the  head  region  (v.  pp.  252,  254),  the  brain  case  is 
cartilaginous,  with,  however,  a  few  true  bone  centres  (e.g. 
epiotic)  appearing;  the  roofs  of  the  skull  and  mouth, 
together  with  the  mandible,  are  well  sheathed  by  dermal 
bones,  as  FP,  N,  PP,  DN,  AG.  Paired  dental  plates 
fringe  the  rim  of  the  mandible  (Fig.  122  A,  M),  the 
vomerine  region  (V),  and  the  anterior  end  of  the  palato- 
pterygoids  (P). 

Fossil  Lung-fishes 

The  structures  of  the  recent  Dipnoans  can  as  yet  be  but 
imperfectly  compared  with  those  of  fossil  forms.  Their 
ancestral  conditions  can  only  be  determined  when  more 


121 


j  2  2  L  UNG-FISHES 

perfect  evidence  is  discovered  as  to  their  kinship  and  the 
lines  W  their  descent. 

In  the  history  of  fishes,  Dipnoans  are  known  to  have  been 
early  a  dominant  group.  In  some  regards,  one  of  their 
ancient  forms  bore  many  resemblances  to  the  Pleura- 
canthid  shark,  which,  although  known  at  present  only  in 
a  later  period,  may  well  have  been  its  contemporary.  But 
the  range  in  the  forms  of  Dipnoans  occurring  in  the  early 
Palaeozoic  indicates  the  remote  antiquity  of  their  origin. 
They  had  even  then  evolved  exoskeletal  characters  which 
are  scarcely  less  specialized  than  those  of  existing  forms. 


Fig.  126.  — A  restoration  of  the  Devonian  lung-fish,  Phaneropleuron.     X  \. 

Dipterus,  of  the  Old  Red  Sandstone  (Fig.  123),  had  a 
complete  body  armouring  of  cycloidal  scales,  a  head  roofing 
of  dermal  plates  (Fig.  124),  and  well-calcified  jaw  rims 
(Figs.  124,  125,  125^4).  Its  fin  rays  were  dermal  in 
structure,  its  paired  fins  were  archipterygial,  its  tail  and 
its  dorsal  fins  separate  and  lobate.  Its  mucous  canals  had 
become  elaborately  adapted  to  the  body  scales  (lateral  line, 
Fig.  123)  and  head  plates,  piercing  the  latter  with  minute 
pores,  as  in  Figs.  65,  66.  Anterior  and  posterior  nares  are 
indicated  under  the  rim  of  the  upper  jaw  (Fig.  125,  1—2). 
Marginal  teeth  have  disappeared ;  a  pair  of  elaborate  dental 
plates  on  the  mouth  roof  (palatine)  are  apposed  by  a  simi- 
lar pair  in  the  hinder  part  of  the  mandible  (splenial). 

The  Carboniferous  Ctenodus  was  a  nearly  allied  form. 

Another  Devonian  lung-fish,  Phaneropleuron  (Fig.  126), 


123 


124 


LUNG-FISHES 


was  similar  to  Dipterus  in  its  skeletal  characters.  Its  elon- 
gate diphycercal  tail  was  continuous  with  the  dorsal  and 
anal  (?)  elements;  in  this,  and  in  the  retention  of  marginal 
cusp-like  teeth,  it  resembled  the  Pleuracanthid  sharks. 

Living  Forms 

The  three  forms  of  living  lung-fishes  may  reasonably  be 
looked  upon  as  the  survivors  of  the  more  generalized  Palaeo- 
zoic forms.  Ceratodus,  the 
Australian  genus,  appears  to 
have  retained  most  perfectly 
the  ancestral  conditions ;  it 
has  probably  remained  almost 
unmodified  from  the  early 
Mesozoic  times,*  and  presents 
close  affinities  to  the  Coal 
Measure  family,  Ctenodontidce, 
and  even  to  the  Devonian 
Dipterids.  Its  outward  ap- 
pearance is  shown  in  Fig. 

127,  and  its  skeleton  in  Fig. 

128.  The  latter  is  seen  to 
resemble  closely  the  charac- 

Fig.   128  A.  — Skull    of    Ceratodus. 
Seen  from    the  ventral    side.      (After    ters    of    Fig.     122;     its    paired 

'ToLpitai  rib.  d.  Dental  plates.  fins    are    archipterygial ;   the 

na.  Anterior  and  posterior  nares.  P.  mouth  is  lacking  in  marginal 
Palatine.  PSph.  Paraspenoid.  Ft.  . 

Pterygoid.  Qu.  Quadrate.     Vo.  Vomer.     Cutting      plates     (cf.      V,      Fig. 

122  A).      The   dental   plates 

of  the  palatine  and  splenial  regions  (Fig.  128  A)  are  seen 
to  correspond  clearly  with  those  of  Figs.  125,  125  A. 

Ceratodus   had   long   been    known  to   the  colonists  of 


r.  p.  10.      The  recent  genus,  according  to  Dr.  Gill,  is  to  be  distinguished 


as  Neoceratodus. 


THE  RECENT  LUNG-FISHES 


125 


Queensland  as  a  plentiful  food-fish,  a  "salmon"  in  size  and 
taste,  although,  curiously  enough,  it  remained  undescribed 
until  1870  (Krefft,  and  Gunther).  After  this  its  develop- 
mental history  was  eagerly  awaited,  in  the  hope  that  it 
would  reveal  the  affinities  of  the  Dipnoans  to  the  sharks, 
amphibians,  and  in  general  to  the  early  chordates.  About 
ten  years  ago  Caldwell  was  sent  to  Queensland  by  the 


Fig.  129. — The  South  American  lung-fish,  Lepidosiren paradoxa,  Natter.     X  £. 
(From  NICHOLSON,  after  NATTERER.)    A  front  view  of  the  mouth  is  shown  at  B. 

Royal  Society,  and  succeeded  in  securing  a  set  of  the 
embryonic  stages,  but  his  results  still  remain  unpublished. 
A  second  set  of  embryos  was  collected  in  1891  by  Semon, 
from  whose  recent  paper  a  summary  is  later  given  (p.  198). 
The  development  of  Ceratodus,  however,  as  far  as  it  is  at 
present  known,  has  proven  in  many  ways  unsatisfactory  to 
the  phylogenist ;  its  abbreviated  growth  stages  cannot  be 


126 


LUNG-FISHES 


looked  upon  as  furnishing  clearly  the  ancestral  history  of 

Dipnoans. 

The  two  remaining  forms  of   recent  lung-fishes,  Lepi- 

dosiren  and  Protopterus, 
resemble  each  other  so 
closely  that  Ayers  has 
contended  that  they 
should  be  regarded  as 
distinct  only  specifically. 
Lepidosiren,  the  South 
American  form  (Fig. 
129),  was  discovered  by 
its  describer,  Natterer, 
in  1837  in  the  upper 
Amazon.  It  then,  for 
many  years,  succeeded 
in  eluding  the  collectors, 
and  was  known  as  one 
of  the  rarest  specimens 
of  foreign  museums.  In 
1887  it  was,  however,  re- 
discovered in  Paraguay, 
where  it  appears  to  have 
long  been  known  as  a 
food-fish.  Its  structures 
are  now  regarded  as  en- 
titling it  unquestionably 
to  the  rank  of  a  distinct 
genus. 

Protopterus,  common 
in  the  White  Nile  and 
Congo  (Fig.  \2()A),  has 
long  been  the  "  Lepido- 


RELATIONSHIPS   OF  LUNG-FISHES  12y 

siren"  of  dealers,  often  of  museums.  It  is  the  best  known 
of  Dipnoans,  on  account,  partly,  of  the  ease  with  which  it 
may  be  transported  alive.  In  the  hardened  mud  cocoons 
with  which  it  encases  itself  during  the  dry  season,  it  is 
readily  dug  out  of  the  stream  bed  and  packed  for  exporta- 
tion. When  placed  in  tepid  water,  the  cocoon  dissolves 
and  the  fish  shortly  revives. 

Relationships 

A  review  of  our  knowledge  of  Dipnoans  gives  but  little 
satisfactory  suggestion  as  to  their  relations  as  a  group. 
They  must  certainly  be  looked  upon  as  an  advancing 
phylum  from  which  the  amphibia  may  early  have  diverged. 
Their  many  amphibian  characters  have  been  lately  em- 
phasized by  W.  N.  Parker.  On  the  other  hand,  the 
evidences  of  the  kinship  of  Dipnoans  to  the  other  types 
of  fishes  can  only  be  interpreted  as  the  common  con- 
vergence of  the  ancient  phyla  toward  the  structures  of  the 
ancestral  form  of  fish.  Thus  we  find  that  the  types  of 
Devonian  lung-fishes  can  only  be  distinguished  from 
those  of  the  contemporary  Teleostomes  by  the  pattern 
of  arrangement  of  the  plates  of  the  head  roof,*  a  condition 
which  has  led  Smith  Woodward  to  believe  that  these 
groups  had  already  diverged  before  the  appearance  of 
dermal  bones. 

Lung-fishes  have  unquestionably  many  structures  which 
may  have  been  derived  from  the  more  generalized  condi- 
tions of  the  sharks  ;  and  as  a  group  they  may  not  unrea- 
sonably be  looked  upon  as  descended  from  the  primitive 
elasmobranchian  stem.  Their  ties  of  kinship  to  the  sharks 

*  The  present  writer  regards  this  distinction  as  somewhat  provisional; 
median  head  plates  are  nominally  characteristic  of  Dipnoans  (Fig.  124),  but, 
as  in  the  sturgeons  and  siluroids,  they  are  also  well  known  among  Teleostomes. 
Protopterus  has,  moreover,  a  symmetrical  arrangement  of  the  head  plates. 


I28  RELATIONSHIPS   OF  LUNG-FISHES 

have  now  been  closened  by  the  proof  that  their  paddle- 
shaped  fins  may  be  directly  deduced  from  a  "monoserial 
archipterygium,"  and  that  their  diphycercal  caudal,  formerly 
regarded  as  most  primitive  in  plan,  may  have  been  acquired 
secondarily  after  a  condition  of  heterocercy  (W.  N.  Parker, 
Traquair,  Dean). 

The  resemblances  of  Dipnoans  to  Elasmobranchs  might 
be  summarized  in  the  following  structures  :  — 

I.  VERTEBRAL    AXIS.      Its    notochordal    condition    and 
simple  metameral,  neural,  and  haemal  elements  suggest  the 
conditions  of  Cladoselache   (p.  80) ;  in  that  ancient  form, 
however,  the  vertebral  processes  had  not  come  into  rela- 
tion with  the  unpaired  fins. 

II.  SKULL.     The  chondrocranium  is  as  yet  largely  re- 
tained ;    as  yet  no  dentigerous  membrane   bones   of   the 
mouth  rim  (maxillary  and  premaxillary)  have  appeared. 

III.  TEETH.     These  are  clearly  of  an  elasmobranchian 
order;  the  tubercles  of  the  dental  plates  (Fig.  125)  suggest 
closely  a  shagreen  pattern  ;   in  Phaneropleuron,  marginal 
cusps  have  even  been  retained.     The  palatine  and  splenial 
plates  parallel  strikingly  some  of  the  forms  of  Cestraciont 
dentition. 

IV.  BRAIN.     Its  structures  are  of  an  advancing  elasmo- 
branchian order,  annectent  with  reptilian  (Ceratodus)  and 
amphibian  types  (Protopterus).* 

V.  VISCERAL  CHARACTERS.    Heart,  gills,  digestive  tract, 
vessels,  mesenteries. 

The  closely  corresponding  characters  of  Phaneropleuron 
and  Pleuracanthus  might  be  looked  upon  as  independently 
acquired ;  but  in  view  of  the  many  nearnesses  of  their 
phyla,  these  characters  may  reasonably  be  regarded  as 
proof  of  genetic  kinship. 

*  Burckhardt. 


ARTHRODIRAN  LUNG-FISHES 

The  advancing  structures  of  the  Dipnoan  include,  in 
addition :  — 

I.  EXOSKELETAL  SPECIALIZATIONS.      Head-roofing  der- 
mal bones  (cf.,  however,  Pleuracanthid)  and  cycloidal  scales. 
In  early  forms  (Dipterus)  these   appeared  at  the  surface 
and    were  apparently  enamelled.     In    recent   forms   they 
are  deeply  sunken  in  the  integument  (Prototerus).     They 
suggest  closely  the  structures  of  Crossopterygian  (p.  149). 

II.  ARTICULATION  OF  THE  MANDIBLE.      This   is   auto- 
stylic,  somewhat  as  in  Chimaeroid  (v.  p.  256).      Its  homol- 
ogy  is  obscure. 

III.  AIR-BLADDER,     (v.  p.  264). 

IV.  ABSENCE   OF  VENTRAL  "CLASPERS"  (cf.,  however, 
Cladoselache). 

V.  TRUE  POSTERIOR  NARES  (amphibian). 

VI.  THE    GREAT   SIZE    OF   THE    CELLULAR   ELEMENTS   OF 

ALL   TISSUES    (amphibian);  THE  GLANDULAR  STRUCTURES 
OF  THE  EPIDERMIS  (amphibian). 

VII.  CIRCULATORY  CHARACTERS  :   the  three-chambered 
heart ;  aortic  arches. 

VIII.  LIMB  STRUCTURE.     This,  however,  is  not  to  be 
interpreted  as  in  any  way  directly  transitional  to  cheirop- 
terygium. 

The  Arthrodiran  Lung-fishes 

The  ARTHRODIRA,  as  Smith  Woodward  has  shown,  may 
provisionally  be  regarded  as  an  order  of  extinct  and  highly 
specialized  lung-fishes.  They  occur  geologically  among  the 
earliest  fishes,  and  include  a  number  of  (Devonian)  forms 
whose  peculiar  characters  and  gigantic  size  must  have  made 
them  among  the  most  striking  members  of  ancient  fauna. 
The  group  might  be  regarded  as  standing  in  the  same  rela- 
tion to  the  ancient  Dipnoan s  as  Acanthodians  to  the  Cla- 


ARTHRODIRAN  LUNG-FISHES 

doselachian  sharks.  As  recently  as  1887  its  members  were 
associated  by  Traquair  with  Pterichthys,  but  the  discovery 
of  jaws,  specialized  dentition,  fin  spines,  and  highly  evolved 
pelvic  fins  at  once  separate  this  group  from  the  lowly 
Ostracoderms. 

American  Arthrodirans,  described  mainly  by  Newberry 
andv  by  Claypole,  have  proven  of  especial  interest.  They 
occur  from  the  Silurian  to  the  Coal  Measures.  The  giant 
predatory  member  of  this  group,  Dinichthys  (Frontispiece, 
and  Figs.  133-137),  attained  a  length  of  ten  feet.  Titan- 
ichtkys,  less  formidable  in  armour  and  dentition,  may  well 
have  been  twenty-five  feet  in  length.  These  forms  occur 
almost  exclusively  in  the  Waverly  of  Ohio.  Their  discovery 
has  here  been  due  to  the  efforts  of  Dr.  William  Clark 
of  Berea,  Rev.  William  Kepler  of  New  London,  and  Mr. 
Jay  Terrell  of  Linton  ;  and  most  of  the  type  specimens 
have  been  preserved  in  the  museum  of  Columbia  College, 
New  York. 

The  European  member  of  this  group  is  a  small,  fresh- 
water (?)  form,  Coccosteus,  especially  abundant  in  the  Old 
Red  Sandstone  of  Scotland.  It  has  thus  far  yielded  the 
most  complete  material  for  study,  and  its  structural  char- 
acters might  accordingly  be  described,  since  they  are 
probably  common  to  all  members  of  the  group. 

The  lateral  view  of  Coccosteus  is  shown  in  Fig.  130,  the 
dorsal  aspect  of  the  anterior  region  in  Fig.  131,  and  the 
ventral  view  of  the  visceral  region  in  Fig.  132.  It  will 
accordingly  be  seen  that  the  general  shape  of  the  body 
of  this  Arthrodiran  was  somewhat  depressed ;  that  the 
head,  shoulder,  and  stomach  regions  were  protected  by 
bony  plates ;  and  that  the  trunk  region  was  lacking  in 
armouring,  and  short  in  relative  length.  In  well-preserved 
fossils  the  space  occupied  by  the  notochord,  N,  is  seen  to 


COCCOSTEUS  I^l 

pass  from  the  region  of  hinder  plates  of  the  body  armour 
to  that  of  the  tip  of  the  tail.  This  is  seen  to  be  bordered 
by  neural  and  haemal  processes,  Nt  Hy  which  in  size  and 
character  are  somewhat  comparable  with  those  of  Protop- 
terus  or  Pleuracanthus.  The  dorsal  fin  presents  a  meta- 
meral  series  of  supporting  cartilages  (radial  and  basal,  DR, 
DB).  The  basal  supports  of  each  pelvic  fin  have  become 
compressed  into  a  flattened  plate,  VB.  Pelvic  fins  were 
present,  but  there  have  as  yet  been  found  no  traces  of 
pectoral  appendages.  In  Dinichthys  Newberry  believed 
that  a  pectoral  fin  spine  was  present,  and  that  this  fin  was 


Fig.  130.  —  The  Devonian  Arthrodiran,  Coccosteus  decipiens,  Agx  X  4.  Old  Red 
Sandstone,  Scotland.  (Side  view,  restored ;  slightly  modified,  after  SMITH  WOOD- 
WARD.) 

A.  Articulation  of  head  with  trunk.  DB,  Cartilaginous  basals  of  dorsal  fin. 
DR.  Cartilaginous  radials  of  dorsal  fin.  H.  Haemal  arch  and  spine.  MC.  Mu- 
cous canals.  A^.  Neural  arch  and  spine.  U.  Median  unpaired  plate  of  hinder 
ventral  region.  VB.  Basals  of  ventral  fin.  VR.  Radials  of  ventral  fin. 

probably  Siluroid-like  (p.  i/i),  but  this  view  has  not  been 
confirmed. 

The  head  of  Coccosteus  was  clearly  flattened,  with 
orbits  and  nasal  openings  near  its  anterior  margin ;  it 
was  roofed  by  a  stout  buckler  of  closely  fitted  dermal 
plates  (Fig.  131),  whose  outer  surface  was  tuberculate, 
enamelled,  and  furrowed  by  sensory  grooves,  MC.  The 
arrangement  of  the  dermal  plates  of  Coccosteus  was  early 
(1861)  compared  by  Huxley  with  that  of  recent  Siluroids, 


132 


AR  THR  ODIRAN  L  UNG-FISHES 


an  analogy  afterward  supported  by  Newberry,  Dean,  and 
recently,  on  account  of  the  similar  characters  of  the  sen- 
sory canals,  by  Pollard.  In  their  conclusions,  however, 
fundamental  characters  of  structure  seem  to  have  been 
overlooked  in  the  unlikeness  of  Arthrodiran  to  Tele- 
ostome.  The  inner  structure  of  the  cranium  of  Arthro- 


PM 


PO 


FIG.  131 


Figs.  131,  132.  —  Coccosteus  decipiens.  Dorsal  view  of  dermal  armouring.  X  J. 
(After  TRAQUAI-R.)  132.  Ventral  plates.  (After  TRAQUAIR.) 

ADL.  Antero-dorso-lateral.  AL.  Anterolateral.  A  VM.  Antero-ventro-lateral. 
C.  Central.  E.  Ethmoid.  EO.  Epiotic.  IL.  Inferior  lateral.  M.  Marginal. 
MC.  Mucous  canals.  MD.  Median  dorsal.  MO.  Median  occipital.  MV.  Me- 
dian ventral.  O.  Opercular.  PDL.  Postero-dorso-lateral.  PL.  Posterior  lateral. 
PM<  Premaxillary.  PN.  Pineal.  PO.  Preorbital.  PTO.  Postorbital.  PVL. 
Postero-ventro-lateral.  SO.  Suborbital. 

dira  was  evidently  entirely  cartilaginous  ;  in  a  Russian 
Coccosteid,  according  to  Smith  Woodward,  the  base  of  the 
brain  case  (parachordal  cartilages)  has  been  preserved  and 
shows  a  "  tubular  canal  originally  occupied  by  the  anterior 


STRUCTURES   OF  ARTHRODIRAN  j^ 

extremity  of  the  notochord."  Gill  arches  and  opercula  are 
not  definitely  known.  The  mandible  was  attached  directly 
to  the  skull  (autostylic).  The  jaws  were  shear-like,  their 
margins  usually  with  pointed  teeth,  whose  bases  fuse  with 
the  tissue  of  the  jaw  and  constitute  dental  plates.  In 
all  forms,  as  in  Dinichthys  (Frontispiece),  there  appear  to 
have  been  three  pairs  of  these  "plates,"  those  forming  the 
rim  of  the  mandible  below,  and  those  of  the  vomerine 
and  palatine  regions  (" premaxillary "  and  "maxillary") 
above.*  This  arrangement  of  the  dental  plates  somewhat 
resembles  the  Dipnoan's.  Those  of  the  Arthrodiran,  how- 
ever, appear  to  have  been  movable,  and  suggest  a  dental 
condition  elsewhere  unknown  among  vertebrates. 


Fig.  133.  —  Restoration  of  Dinichthys  intermedius,  Newb.  X  &.  Cleveland 
Shales,  Ohio. 

The  body  armouring  of  dermal  plates  is  characteristic  of 
the  group.  A  carapace,  cape-like  in  shape,  begins  at  the 
head  angle  and  broadens  out  backward  and  dorsally 
towards  the  median  line.  It  consists  of  a  single  median 
spade-shaped  element,  which  forms  the  strong  ridge  of  the 
back,  and  a  flanking  of  lateral  plates,  all  compactly  joined. 
The  rigid  shield  that  is  thus  formed  is  movably  connected 
with  the  head ;  an  elaborate  joint,  formed  on  either  side 
between  the  anterolateral  dorsal  plate,  Fig.  131,  ADL,  and 
the  "epiotic,"  EO, — whence  the  name  Arthrodira, —  must 

*  According  to  Dr.  Clark,  an  additional  symphysial  pair  of  dental  plates 
was  present  in  both  upper  and  lower  jaw  (Dinichthys). 


134 


AR  THR  ODIRAN  L  UNG-FISHES 


have  permitted  the  head  to  be  thrown  backward  to  a 
degree  which  suggests  the  thoracic  joint  of  an  Elater. 
On  the  ventral  side  of  the  trunk  there  occurs  a  flattened 
plastron  (Fig.  132) :  its  dermal -elements  are  connected  by 
overlapping  margins ;  they  are  lighter,  and  in  some  forms 
(Fig.  135)  lack  the  tuberculate  surface  of  the  dorsal 
plates.  Dorsal  and  ventral  shields  are  connected  by  stout 
lateral  elements  (Fig.  132,  7Z),  which,  passing  ventrally, 


FIG.  135 


137  A 


Figs.  134-137.  —  Dermal  plates  of  Dinichthys.  134.  Associated  plates  of  head 
and  shoulders.  135.  Plates  of  ventral  armouring.  (After  A.  A.  WRIGHT).  136. 
Pineal  plate  of  Dinichthys  intermedius,  surface  view.  137.  Pineal  plate  of  Dinich- 
thys terrelli,  visceral  aspect.  137  A.  Pineal  plate,  in  sagittal  section. 

ADL.  Antero-dorso-lateral.  A  VL.  Antero-ventro-lateral.  A  VM.  Antero- 
ventro-median.  E.  Ethmoid.  EO.  Epiotic.  MO.  Median  occipital.  PN. 
Pineal.  PO.  Preorbital.  PTO.  Postorbital.  PVL.  Postero-ventro-lateral.  SO. 
Suborbital.  X.  External  aperture,  and  -*• ,  the  axis  of  the  pineal  funnel. 

meet  in  the  median  line,  and  become  the  anterior  support- 
ing rim  of  the  plastron.  By  some  writers  these  have  been 
homologized  as  "  clavicles." 

In   further   detail   little   is   known  of   the  anatomy  of 


STRUCTURES   OF  ARTHRODIRAN 


135 


Arthrodirans.  Sensory  canals  have  been  described  chan- 
nelling the  surface  of  the  dermal  plates  of  the  dorsal  side. 
In  the  body  region  of  Coccosteus  evidence  of  a  lateral  line 
occurs  (Smith  Woodward)  in  a  white  calcified  band  fossilized 
in  the  region  of  the  space  of  the  notochord.  In  this  form, 
too,  an  endoskeletal  plate  is  known,  (Fig.  130,  U)  occurring 
in  the  median  line  in  the  region  of  the  vent,  which  must 
be  regarded  as  "  suggesting  an  internal  element  of  support 
occurring  in  the  vertical  septum  between  the  right  and 
left  halves  of  some  paired  organ  (S.  W.)."  The  character 
of  the  dermal  investiture  of  the  trunk  has  apparently 
not  been  described ;  it  may  therefore  be  of  interest  to 
note  that  the  museum  of  Columbia  College  has  recently 
acquired  two  of  the  hinder  dorsal  plates  of  Dinichthys 
which  clearly  indicate  the  presence  of  integument.  The 
plates  are  covered  by  a  crinkled  epidermis,  whose  irregular 
surface  traceries  resemble  the  roughened  finish  of  Turkey 
morocco.  This  leather-like  surface  is  seen  to  have  been 
continued  over  the  margin  of  the  plates  along  the  side 
of  the  trunk ;  traces  of  scales  or  tubercles  are  altogether 
lacking,  and  its  appearance  suggests  that  it  may  have  been 
degenerate  in  structure. 

Among  Arthrodirans  there  occurs  a  series  of  most  inter- 
estingly evolved  forms ;  and  it  is  found  more  and  more 
evident  that  they,  with  other  lung-fishes,  may  have  repre- 
sented the  dominant  group  in  the  Devonian  period,  as 
were  the  sharks  in  the  Carboniferous,  or  as  are  the 
Teleosts  in  modern  times.  There  were  forms  which, 
like  Coccosteus,  had  eyes  at  the  notches  of  the  head 
buckler;  others,  as  Macropetalichthys,  in  which  orbits 
were  well  centralized  ;  some,  like  Dinichthys  and  Titan- 
ichthys,  with  the  pineal  foramen  present ;  some  with 
pectoral  spines  (?) ;  some  with  elaborately  sculptured  derm 


136 


AR  THR  ODIRAN  L  UNG- FISHES 


plates.  Among  their  forms  appear  to  have  been  those 
whose  shape  was  apparently  sub-cylindrical,  adapted  for 
swift  swimming ;  others  (Mylostomd)  whose  trunk  was 
depressed  to  almost  ray-like  proportions.  In  size  they 
varied  between  that  of  a  perch  and  that  of  a  basking 
shark.  In  dentition  (Figs.  138-144)  they  presented  the 
widest  range  in  variation,  from  the  formidable  shear-like 
jaws  of  Dinichthys  to  the  lip-like  mandibles  of  Titan- 
ichthys,  the  tearing  teeth  of  Trachosteus,  the  wonderfully 
forked,  tooth-bearing  jaw  tips  of  Diplognathus,  to  the 
Cestraciont  type,  Mylostoma.  The  latter  form  has  hitherto 
been  known  only  from  its  dentition,  but  now  proves  to  be, 
as  Newberry  and  Smith  Woodward  suggested,  a  typical 
Arthrodiran. 

The  puzzling  characters  of  the  Arthrodirans  *  do  not 
seem  to  be  lessened  with  a  more  definite  knowledge  of 
their  different  forms.  The  tendency,  as  already  noted, 
seems  to  be  at  present  to  regard  the  group  provisionally  as 
a  widely  modified  offshoot  of  the  primitive  Dipnoans,  bas- 
ing this  view  upon  their  general  structural  characters, 
dermal  plates,  dentition,  autostylism.  But  only  in  the 
latter  regard  could  they  have  differed  more  widely  from 
the  primitive  Elasmobranch  or  Teleostome,  if  it  be  ad- 
mitted that  in  the  matter  of  dermal  structures  they  may 
clearly  be  separated  from  the  Chimaeroid.  It  certainly 
is  difficult  to  believe  that  the  articulation  of  the  head  of 
Arthrodirans  could  have  been  evolved  after  dermal  bones 
had  come  to  be  formed,  or  that  a  Dipnoan  could  become 
so  metamorphosed  as  to  lose  not  only  its  body  armouring 

*  The  writer  believes  that  the  Arthrodirans  may  as  well  be  referred  to  the 
sharks  as  to  the  lung-fishes;  as  far  as  existing  evidence  goes,  they  certainly 
differed  more  widely  from  the  lung-fishes  than  did  the  lung-fishes  from  the 
ancient  sharks.  They  may,  perhaps,  be  ultimately  regarded  as  worthy  of  rank 
as  a  class. 


FIG.  138 


144 


Figs.  138-144.  —  Mandibles  of  Arthrodirans :  Cleveland  Shale,  Ohio.  138. 
Mylostoma  variabllis,  Xewb.,  visceral  aspect.  139.  Titanichthys  clarki,  Newb., 
visceral  aspect,  x  g.  140.  Trachosteus,  Newb.,  outer  aspect.  X  5.  141.  Diplo- 
gnathus,  Newb.,  outer  aspect.  X  J.  142.  Diplognathus,  seen  from  dorsal  side. 
143.  Diplognathns,  visceral  aspect.  144.  Dinichthys  intermedius,  outer  aspect.  X  5. 

137 


ARTHRODIRAN  LUNG-FISHES 

but  its  pectoral  appendages  as  well.  The  size  of  the 
pectoral  girdle  is,  of  course,  little  proof  that  an  anterior 
pair  of  fins  must  have  existed,  since  this  may  well  have 
been  evolved  in  relation  to  the  muscular  supports  of 
plastron,  carapace,  trunk,  and  head.  The  inter-movement 
of  the  dental  plates,  seen  especially  in  Dinichthys,  is  a 
further  difficulty  in  accepting  their  direct  descent  from 
the  Dipnoans. 


VII 
THE  TELEOSTOMES 

ALL  fishes  not  to  be  grouped  among  Sharks,  Chimae- 
roids  or  Lung-fishes,  have  been  included  in  the  fourth 
sub-class,  Teleostomi.  In  this  are  to  be  merged  the  two 
time-honoured  groups,  Ganoids*  and  Teleosts,  since  it  is 
now  found  that  there  are  absolutely  no  structures  of  the 
one  group  that  are  not  possessed  by  members  of  the  other. 
The  terms,  therefore,  "Ganoid"  and  "Teleost,"  must 
be  used  in  a  popular  and  convenient,  rather  than  in  an 
accurate  sense  ;  the  former  to  denote  the  "  old-fashioned  " 
Teleostome,  with  its  rhombic  bony  body  plates,  and  carti- 
laginous endoskeleton ;  the  latter,  the  modern  "bony  fish," 
with  rounded,  horn-like  scales  and  its  calcified  endo- 
skeleton. 

Teleostomes  present  so  wide  a  range  of  variation  that 
it  becomes  exceedingly  difficult  to  include  in  a  single 
definition  their  minor  structural  characters. 

As  a  basis  for  the  comparison  of  the  Teleostomes,  the 
characteristic  structures  of  a  single  type,  e.g.  the  Perch, 
might  conveniently  be  taken.  From  these  conditions, 
typical  of  a  modern  and  highly  specialized  form,  the  simple 
structures  of  the  ancient,  more  primitive,  and  ancestral 
Ganoids  may  afterward  be  readily  understood. 

*  The  term  Ganoid,  as  here  vised  (as  far  as  p.  147),  includes  the  Crossopte- 
rygians  as  well. 

139 


140 


STRUCTURES   OF  TELEOST  l^l 

General  Anatomy 

In  the  Teleost  (Fig.  145)  the  shortened  and  muscular 
body  appears  admirably  adapted  to  the  conditions  of 
aquatic  motion.  Anteriorly  it  is  broad  and  deep,  its 
trunk  muscles  firmly  attached  to  the  bony  prongs  of  the 
enlarged  base  of  the  skull,  DCR,  and  to  the  solid,  compact, 
calcified  vertebrae,  V,  and  their  stout  processes.  The 
fish's  tapering  sides  are  encased  in  horn-like  cycloidal 
scales,  CS,  a  light,  flexible  armour,  whose  elements  over- 
lap, defending  every  point,  and  whose  smooth  and  slime- 
coated  surface  provides  the  least  possible  resistance  to 
motion.  The  fins,  D,  C,  A,  PFy  VF,  are  light  and  strong, 
erectile  and  depressible ;  their  rays  are  thin,  narrow,  spine- 
like,  strong ;  they  are  entirely  dermal,  their  cartilaginous 
supports  sinking  within  the  body  wall,  RB.  The  caudal 
is  large  and  fan-shaped  (homocercal),  its  crowded  rays 
providing  admirably  its  needed  strength ;  its  stout  basal 
supports,  compacted  beneath  the  tip  of  the  notochord,  JVC, 
show  that  its  form  is  modified  heterocercy.  The  pectoral 
fin,  PFt  has  now  taken  its  position  high  in  the  side  of  the 
body ;  its  basi-radial  supporting  elements  are  reduced  to  a 
proximal  row  of  a  few  small  irregular  plates. 

The  skeleton  is  completely  calcified.  The  vertebral  axis 
has  undergone  entire  segmentation,  the  notochord  persist- 
ing only  between  the  cup-shaped  faces  of  the  centra ;  the 
vertebral  arches  and  processes  have  merged  with  the 
centra,  and  those  of  the  hinder  region,  A7,  H,  with  prob- 
ably the  basal  fin  supports  as  well.  Ribs,  R,  usually  with 
intersupporting  processes,  strengthen  the  walls  of  the 
visceral  cavity,  and  represent  calcifications  of  the  myocom- 
mata,  rather  than  transverse  processes  of  the  vertebrae. 
The  skull  is  formed  of  compact  bony  elements ;  its  carti- 


" 


fl    l 

a    1  14  8 


STRUCTURES  OF  TELEOST  I43 

laginous  brain  case  is  replaced  by  many  definite  osseous 
•elements.  The  floor  and  roof  of  the  skull,  the  face  region, 
jaws,  gill  arches,  and  their  protecting  parts,  are  all  encased 
by  an  elaborate  series  of  membrane  bones  ;  these,  however, 
must  be  noted  as  deeply  embedded  in  the  body  tissue, 
DCR,  DN,  A,  Q,  PT,  SM,  BR,  O.  The  membrane  bones 
of  the  jaw  rim  —  maxillary,  premaxillary,  and  dentary,  MX, 
PMX,  DN —  bear  teeth,  and  are  especially  characteristic 
of  the  Teleostomes  ;  those  overlapping  and  protecting  the 
gill  arches  (GA),  O,  fO,  PO,  SO,  usually  four  in  number, 
are  also  characteristic  of  the  group.  The  skull  is  hyostylic. 
As  to  the  visceral  parts.  The  gill  arches,  GA,  are 
reduced  in  number,  usually  widely  bent  backward,  and 
closely  crowded  together ;  their  gill  filaments  are  enlarged 
and  specialized.  The  heart  lacks  the  arterial  cone  with  its 
transverse  series  of  valves ;  in  its  place  a  stout  bulbus,  B, 
forms  the  base  of  the  aorta.  The  digestive  tract  is  tubular, 
long,  and  coiled ;  its  intestine,  G,  lacks  a  spiral  valve,  and 
terminates  at  the  body  surface,  AN,  not  in  a  cloaca ;  its 
glands  include  a  series,  often  great  in  number,  of  pyloric 
caeca  (pancreas).  An  air-bladder,  AB,  is  present,  which 
may,  or  may  not,  retain  its  communication  with  the  gullet. 
The  ovary,  with  its  many  small  eggs,  and  the  kidney,  dorsal 
to  it,  have  often  a  common  external  opening  in  a  urino- 
genital  papilla,  UG,  in  either  side  of  which  abdominal  pores 
may  occur.  The  nervous  system  and  sense  organs  (pp.  275, 
277)  have  many  peculiarities  :  the  roof  of  the  fore  brain  is 
non-nervous  ;  the  nasal  openings  appear  in  the  dorsal  side 
of  the  head,  NO,  and  are  separate;  the  eye  has  specialized  a 
vascular,  nutritive  structure,  \hzproctssusfalciformis,  pro- 
jecting from  the  region  of  the  entrance  of  the  optic  nerve 
into  the  vitreous  cavity  of  the  capsule ;  the  optic  nerves 
cross  in  passing  to  the  eyes,  but  their  fibres  do  not  fuse. 


144 


TELEOSTOMES 


Such  in  outline  are 
the  essential  structures 
ofaTeleost.  They  may 
now  be  briefly  con- 
trasted with  the  more 
important  characters  of 
the  Ganoids. 

In  skeletal  structures 
the  Perch  (Fig.  146) 
may  be  strikingly  con- 
trasted with  the  most 
nearly  ancestral  form 
of  Ganoid  (Fig.  147). 
In  this,  Polypterus  (p. 
148),  the  skeleton  re- 
.tains  a  semi-calcified 
condition.  Its  verte- 
bral centra  are  practi- 
cally separate  from  the 
arches  ;  its  ribs,  R,  are 
equivalent  to  the  trans- 
verse processes ;  its  ac- 
cessory ribs,  AR,  to 
the  "ribs "of  Teleosts. 
The  cartilaginous  brain 
case  is  notably  re- 
tained; the  membrane, 
or  dermal  bones,  of  the 
head  roof,  as  F,  P,  SP, 
PO,  O,  are  clearly 
scale -like,  with  an 
enamelled  surface,  sim- 
ilar in  character  to 


GANOIDS  AND    TELEOSTS 


145 


those  of  Dipterus.  The  shoulder  girdle  includes  outer 
dermal  elements,  DSG.  The  external  parts  of  the  unpaired 
fins  are  dermal;  but  their  cartilaginous  supports  are  re- 
tained, RB,  even  in  the  tail  region.  The  caudal  fin  may 
be  regarded  as  either  diphycercal  or  heterocercal.  The 
exposed  parts  of  the  paired  fins,  it  is  especially  interesting 
to  note,  are  only  in  part  dermal ;  the  two  rows  of  carti- 
laginous supports  are  retained  in  a  condition  very  similar 
to  that  of  sharks,  R  B\*  two  of  the  basal  elements  of  the 
pectoral  fin,  however,  have  retained  the  rod-like  form  in 
strengthening  the  front  and  hinder  margin  of  the  fin. 

In  visceral  structures  the  Ganoids  exhibit  the  fol- 
lowing noteworthy  characters :  a  greater  number  of  gill 
arches  ;  a  spiracle ;  a  short  and  almost  straight  digestive 
tube,  with  spiral  valved  intestine ;  a  shark-like  pancreas ; 
an  arterial  cone,  with  many  rows  of  valves ;  a  cellular  air- 
bladder,  like  that  of  a  Dipnoan  ;  primitive  conditions  in  the 
urinogenital  apparatus ;  shark-like  characters  in  the  ner- 
vous system  and  sense  organs ;  a  chiasma  of  the  optic 
nerves,  (pp.  260-279). 

Relationships  and  Descent 

Johannes  Miiller,  when  separating  Ganoids  from  Tele- 
osts,  recognized  clearly  even  at  that  early  date  (1844)  that 
the  majority  of  the  structural  differences  of  these  forms 
were  bridged  over  in  exceptional  instances ;  there  were 
thus  Teleosts  with  bony  body  plates,  as  well  as,  it  was 
afterwards  found,  a  Ganoid  (Amta,  p.  163)  with  herring- 
like  cycloidal  scales.  But  he  believed  that  three  structural 
characters  of  the  Ganoids  separated  them  constantly  from 
all  Teleosts,  and  warranted  the  integrity  of  the  groups. 

*  Contrast  Gegenbaur's  view  that  this  fin  represents  the  simplest  known 
condition  of  the  archipterygium.     Ref.  on  p.  248. 
L 


TELEOSTOMES 

These  distinguishing  characters  were  :  — 

I.  A  contractile  arterial  cone,  containing  rows  of  valves. 

II.  An  intestinal  spiral  valve. 

III.  The  interfusion  (chiasma)  of  the  optic  nerve. 

It  was  not  until  these  differences  were  shown  to  be  of 
little  morphological  importance  that  the  two  groups  were 
merged  in  that  of  Teleostomi  (Owen,  1866).  Thus  transi- 
tional characters  in  the  arterial  cone  of  Butrinus  (p.  258) 
were  discovered  by  Boas  :  the  Teleost  Cheirocentrus  was 
found  to  present  ganoidean  intestinal  characters ;  and  the 
optic  chiasma,  as  Wiedersheim  *  demonstrated,  could  no 
longer  be  regarded  as  of  taxonomic  or  morphological 
value. 

The  descent  of  the  Teleostomes,  likefthat  of  the  other 
groups,  has  long  been  a  matter  of  speculation.  Their  affini- 
ties with  the  Dipnoans  are  generally  admitted  (Gunther, 
Gegenbaur,  Haeckel,  Smith  Woodward).  Rabl  derives  them 
directly  from  a  selachian  stem,  regarding  the  Dipnoans 
as  later  evolved  ganoidean  forms.  Beard,  on  the  other 
hand,  even  goes  so  far  as  to  entirely  separate  the  Teleo- 
stome  stem  from  that  of  the  shark,  lung-fish,  and  amphibian, 
deriving  it  with  a  close  kinship  to  Petromyzonts,  from  the 
earliest  vertebrates.  Palaeontology,  however,  has  lately 
been  giving  rich  contributions  to  this  disputed  problem, 
and  there  can  at  present  be  little  doubt  that  the  conditions 
in  fossil  fishes  have  demonstrated  that  in  most  ancient 
times  Dipnoan  and  Teleostome  were  closely  approximated. 
Although  even  in  the  earliest  fossils  they  may  be  distin- 
guished (e.g.  by  the  arrangement  of  the  head-roofing  derm 
bones,  v.  p.  127),  yet,  as  Smith  Woodward  has  noted,  forms 
occur  too  clearly  transitional  to  indicate  anything  less 

*  One  form  of  lizard  was  shown  to  possess  a  chiasma  of  the  optic  nerves; 
in  its  neighbouring  genus  the  nerves  were  found  to  cross  without  fusion. 


INTERRELATIONSHIPS   OF  TELEOSTOMES 

than  genetic  kinship.  The  Crossopterygian,  whose  ancient 
structure  is  well  known,  may  well  have  been  derived  from 
an  ancestor  common  to  the  Ctenodont  (Dipnoan)  and 
Holoptychian  (Fig.  153) ;  so  that  the  gradual  nearing  of  the 
Teleostome  stem  to  that  more  fixed,  of  the  Dipnoan,  is  a 
strong  suggestion  as  to  its  derivation.  The  later  descent 
of  the  Ganoids  from  an  ancestor  closely  akin  to,  if  not 
identical  with  the  Crossopterygian,  is  usually  conceded. 
Teleosts  first  occurring  in  Cretaceous  are  by  evidence  of 
fossils  the  almost  undoubted  survivors  of  an  extensive 
group  of  transitional  Mesozoic  Ganoids  (p.  165).  But 
whether  all  Teleosts  are  to  be  deduced  from  a  single 
ganoidean  phylum  can  at  present  hardly  be  established. 
Thus  catfishes,  or  Siluroids,  appear  in  many  structural 
regards  closely  akin  to  the  .sturgeon  (p.  160) ;  but  as  their 
fossil  remains  are  lacking  before  the  Eocene — when,  how- 
ever, they  appear  to  have  been  in  every  way  as  highly 
evolved  as  in  recent  forms  —  little  clue  has  been  given  to 
their  descent. 

Teleostomes  may,  in  the  present  connection,  be  briefly 
characterized  under  their  two  principal  subdivisions. 

I.  CROSSOPTERYGIAN,  the  more  archaic  group,  uniting 
characters  of  shark,  lung-fish,  and   Ganoid,  retaining  the 
ancient  cartilaginous  fin  bases,  radials,  and  basals  in  their 
lobate  fins;  in  some  forms  (Holoptychius,   Fig.    153),  the 
concrescence  of  the  basal  parts  of  unpaired  fins  passing 
through    the    same    evolution    as    those    of    paired    fins. 
Represented    in    the    surviving    Polypterus    ("  Bichir "    of 
the  White  Nile,  Fig.  148),  and  in  the  slender  Polypteroid 
Calamoichthys  (of  Calabar),  and  in  the  extinct  Holoptych- 
ius, Undina,  Diplurus,  and  Coelacanthus. 

II.  ACTIXOPTERYGIAN,    the    spine-finned    Teleostomes. 
Fins  supported  by  dermal  rays  ;  ancient  fin  support  greatly 


148 


TELE  OS  TOMES 


Fig.  148. 
bichir.     x  J. 


The    Nile    bichir,   Polypterus 
White   Nile.     (Modified  after 


Dors    aspect.   B.  view  of  throat  re- 

gion,  showing  jugular  (gular)  plates  and  ven- 
tral elements  of  the  dermal  shoulder  girdle. 


reduced,  implanted  with- 
in body  wall.  Includes 
Chondrosteans  ("  Gan- 
oids ")  and  Teleocephali 
("  Teleosts  "). 

I.   CROSSOPTERYGIANS 

The  CROSSOPTERYG- 
IANS, as  palaeontology 
has  demonstrated,  are 
the  most  ancient  Tele- 
ostomes.  In  their  struct- 
ural characters  —  espe- 
cially in  the  fins,  skeleton, 
nervous  system  —  they 
are  clearly  to  be  sepa- 
rated from  the  neigh- 
bouring Ganoids.  And 
their  transitional  charac- 
ters have  not  as  yet  been 
clearly  demonstrated. 

Polypterus  (Figs.  148, 
A,  B,  149)  and  its  kindred 
genus,  Calamoichthys 
(Fig.  150),  stand  alone 
as  the  survivors  of  the 
Crossopterygian  group. 
They  have  diverged  but 
little  from  their  Devo- 
nian kindred,  and  demon- 
strate in  the  most  inter- 
esting way  the  persistent 
survival  of  fishes.  From 


RECENT   CROSSOPTERYGIAN 


149 


their  isolated  position,  these  recent  forms  become  of  ex- 
treme interest  to  the  morphologist,  and  from  the  side  of 
their  development,  when  this  comes  to  be  studied,  they  are 
expected  to  throw  the  greatest  light  on  the  relations  of  the 
primitive  Teleostome  to  the  sharks  and  Dipnoans,  on  the 
one  hand,  and  to  the  Ganoids  on  the  other. 

Polypterus  *  presents  the  exoskeletal  characters  of  the 
ancient  Crossopterygians,  and  the  typical  conditions  of 
their  lobate  pectoral  fins;  the  dermal  plates  of  its  head 
region  are  tuberculate  as  in  Dipnoans,  but,  unlike 
these,  their  arrangement,  as  in  all  Teleostomes,  is  dis- 


Fig.  149.  —  Polypterus   lapradei.     (After   STEINDACHNER.) 
well-grown  larva  showing  external  gill,  EG. 


Head  region  of 


tinctly  paired,  i.e.  "ethmoids,"  frontals,  parietals,  occipi- 
tals  (Fig.  148  A),  including  a  pair  of  gular  plates  in  the 


throat  region, 


Among  the  structures  peculiar  to  the 


*  Polypterus  occurs  in  the  Nile,  but  is  rarely  taken  below  the  Cataract.  It 
was  noted,  however,  from  near  Cairo  in  the  Description  d"1  Egvpte,  and  a  spec- 
imen in  the  possession  of  Professor  Innes  of  the  College  of  Medicine,  Cairo,  was 
taken  near  Boulak  a  few  years  ago.  It  is  known  by  the  Arabs  near  Assuan, 
and  is  here  occasionally  taken  in  the  fykes  at  the  beginning  of  the  flooding- 
season.  The  remarkable  series  of  Polypterus  in  the  Vienna  collection  was 
collected  in  the  White  Nile,  although  some  of  these  specimens,  Dr.  Stein- 
dachner  has  stated  personally  to  the  writer,  were  taken  in  Middle  Egypt.  It 
seems  evident  to  the  writer,  from  the  results  of  his  collecting-trip  from  Cairo 
to  Assuan,  April  and  May,  1892,  that  abundant  material  of  Polypterus  is  not 
readily  secured  below  the  Second  Cataract.  Until,  therefore,  the  interior  of 
Egypt  is  made  more  accessible  to  foreigners,  developmental  stages  can  hardly 
be  hoped  for. 

f  As  in  some  of  the  fossil  lung-fishes. 


jj  0  TELE  OS  TOMES 

recent  forms  may  be  included  the  fringing  dor- 
sal fin,  the  tubular  nasal  opening  (Fig.  149), 
and  an  external  gill  in  Polypterus  (Steindach- 
ner),  EG,  in  the  late  larval  stages. 

Calamoichthys  is  unquestionably  a  divergent 
member  of  the  stem  of  Polypterus ;  its  form, 
becoming  elongated,  has  acquired  a  general  un- 
dulatory  movement ;  the  paired  fins  have  accord- 
ingly  diminished  in  relative  size,  the  ventral  fins 

g,     finally  disappearing. 

Little  is  known  of  either  the  living  or  breed- 

^     ing  habits  of  Crossopterygians  :   in  these  they 
might  naturally  be  expected  to  resemble  the 

Ganoids. 

| 

Fossil  Crossopterygians 


A  number  of  the  fossil  kindred  of  Polypterus 
"I     are  shown  in  the  succeeding  figures  (Figs.  151- 


\          Gyroptychius  and  Osteolepis,  Devonian  genera 
g>     (Figs.    151,    152),  are  certainly  most  nearly  in 

JSP    the  ancestral  line  of  the  recent  forms.      Like 
pjj 

many  sharks  and  fossil  Dipnoans,  they  present 
a  heterocercal  tail,  a  single  anal  fin,  and  a  pair 
of  dorsals.  The  pectoral  fin  of  Osteolepis  is 
becoming  a  typical  archipterygium. 

Holopty  chins,   another   Devonian    form    (Fig. 
153),  approaches  even  more  closely  the  dipnoan 
types  :  the  scales  are  cycloidal  ;  its  paired  fins 
IP  are  distinctly    archipterygial  ;    and    the    caudal 

region,  reduced  in  length,  is  becoming  meta- 
morphosed into  the  typical  diphycercal  form  by  the  ten- 
dency of  the  second  dorsal  and  anal  fin  to  coalesce  with 


FOSSIL    CROSSOPTERYGIANS  jjjj 

the  caudal.      In  these  forms  a  number  of   paired   gular 
plates  may  occur. 

In    a    closely    related    genus,    Eusthenopteron,    also    of 


Fig.  151 


152 


Fig.  i^i.—  Gyroptychius.  x  \.  Old  Red  Sandstone,  Scotland.  (After  SMITH 
WOODWARD.) 

Fig.  152.  —  Osteolepis.  X  4.  Old  Red  Sandstone,  Scotland.  (Restoration 
from  SMITH  WOODWARD,  after  PANDER.) 

Devonian  age  (Fig.  154,  A,  £),  the  structure  of  the  basal 
parts  of  the  unpaired  fins  is  exceedingly  interesting ;  the 
radial  supports  are  unfused,  while  the  basals,  merged  in  a 


Fig.  153.  —  Holoptychius  andersoni.     Old  Red  Sandstone,  Scotland. 

single  plate,   have   come   into   especial   relation  with   the 
axial  skeleton ;  the  subsequent  stage  of  their  differentia- 


FOSSIL    CROSSOPTERYGIANS 


153 


tion  has  been  noticed  in  Fig.  43.  The  condition  of  the 
caudal  fin  of  Eusthenopteron  is  also  worthy  of  note ;  the 
tip  of  the  notochord  is  retained  although  the  functional 
portion  of  the  fin  is  derived  from  the  more  anterior 
body  region.  The  vertebral  arches  are  here  clearly  sug- 
gestive of  the  conditions  of  the  Dipnoan. 

CcflacantkuS)  common  in  the  Coal  Measures  (Fig.  155), 
is  the  most  specialized  of  the  Crossopterygians ;  it  has 
retained  all  of  the  archaic  structures  of  its  kindred,  yet 
has  concealed  them  under  the  outward  appearance  of  a 
recent  bony  fish ;  the  general  contours  of  its  head,  trunk, 
scales  and  fins  resemble  strikingly  those  of  a  dace  or 


Fig.  155.  —  Ceelacanthus  elegans,  Newb.     x  |.    Coal  Measures,  Ohio. 
A.  Position  of  calcified  swim-bladder. 

chub ;  but  on  closer  view  the  paired  fins  are  found  to  be 
archipterygial,  the  scales  enamelled  and  sculptured,  the 
true  caudal  fin  the  degenerate  stump  of  the  notochord ; 
the  functional  caudal  has  been  formed  of  the  enlarged  fin 
rays  of  the  dorsal  and  anal  region.  Traces  of  a  calcified 
air-bladder,  A,  are  often  preserved. 

Diplurus  and  a  closely  related  genus,  Undina  (Figs  156, 
156  A),  may  finally  be  noted  among  the  highly  evolved 
Crossopterygians.  They  appear  in  the  Mesozoic  when  the 
majority  of  their  kindred  have  disappeared  ;  they  have  as- 
sumed peculiar  characters  and  have  apparently  reached  the 
point  of  differentiation  when  they  shortly  become  extinct. 


154 


TELEOSTOMES 


Diplurus  has  become  excessively  shortened  in  its  body 
length ;  the  head  is  of  relatively  enormous  size ;  its  derm 
bones  are  squamous,  and  appear  to  have  been  deeply 
implanted  in  the  integument ;  teeth  have  disappeared ; 


Fig.  156.  —  Diplurus  longicaudatus ,  Newb.     X  \.    Triassic,  Boonton,  NJ. 

A.  Position  of  calcified  swim-bladder.  A" '.  Second  anal  fin  (now  the  ventral 
portion  of  the  functional  caudal) .  BR.  Radial  and  basal  fin  supports.  C.  Caudal 
fin  (degenerate).  D,  Hindmost  dorsal  fin  (now  the  dorsal  portion  of  the  func- 
tional caudal).  J.  Jugular. 

scales  have  become  exceedingly  thin  and  are  rarely  pre- 
served. Fin  structures  are  apparently  of  a  degenerate 
character ;  their  cartilaginous  bases,  when  showing,  appear 


Fig.  r$6  A.  —  Undina    gulo,    Egert. 
(Restoration  after  SMITH  WOODWARD.) 


Lower    Lias    of   Lyme    Regis. 


to  have  become  reduced  to  single  plates,  as  BR ;  the 
caudal  is  the  elongate  tip,  of  the  vertebral  axis ;  the 
functional  caudal,  now  elongate  and  diphycercal,  is  formed 


CAN  OWE  AN  FORMS  !^ 

by  dorsal  and  anal  elements,  D,  A"y  as  in  Coelacanthus. 
The  boundary  line  of  the  calcified  air-bladder,  A,  is  often 
preserved. 

II.    ACTINOPTERYGIANS 

A.  Chondrosteans  (Ganoids}.  Ganoids  agree  with  the 
Crossopterygians  in  their  exoskeletal  characters,  although 
usually  lacking  in  gular  plates.  The  most  important 
differences  between  these  groups  have  been  reduced  to 
those  of  fin  structures ;  the  Ganoids  have  no  longer  the 
lobate  form  of  the  paired  fins ;  their  basal  fin  supports 
have  become  greatly  reduced  and  are  usually  represented 
by  a  single  row  of  a  few  metamorphosed  elements  in  the 


Fig.  157.  —  The  short-nosed  gar-pike,  Lepidosteus platystomus,  Raf.  x  \.  Mis- 
sissippi basin.  (After  GOODE  in  U.  S.  F.  C.) 

most  proximal  region  of  the  fin.     The  transitional  stages 
—  if  they  exist  —  between  the  lobate  and  the  monoserial 
fins  have  not  as  yet  been  demonstrated. 

Fossil  Forms 

From  the  middle  of  the  Palaeozoic  period  to  the  end  of 
the  Mesozoic  there  seems  to  have  been  a  culminating  time 
of  forms  like  the  still  existing  Gar-pike  (Fig.  157);  their 
fossils  are  generally  the  most  numerous,  and,  on  account 
partly  of  their  strong  body  armouring  of  interlocking 
rhombic  plates,  the  most  perfectly  preserved  of  fossil 
fishes.  They  usually  exhibit  the  structural  characters 


TELEOSTOMES 


which  Lepidosteus  has  retained,  while  diverging  widely  on 
all  sides  in  matters  of  shape,  size,  special  dentition,  and 


Fig.  158.  —  Elonichthys    (Kkabdolepis)    macropterus    (Giebel),    Bronn.     x  \. 
(After  L.  AGASSIZ.)     Lower  Permian,  Rhenish  Prussia. 

features  of  the  body  armouring,  —  characters,  apparently, 
of  minor  morphological  importance.  But  a  few  of  the  char- 
acteristic types  of  the  early  Ganoids  can  be  noted  in  the 
present  connection.  Some  of  the  more  important  have 
been  figured  in  Figs.  158-164. 


ig-  159-  —  Eurynotus  crenatus,  Agassiz.     x  £.     (After   TRAQUAIR.)      Calcif- 
erous  Limestone,  Scotland. 

Thus    Elonichthys   (Fig.    158)   was   a   form   which    had 
evolved  a  small  size  and  narrow  sculptured  body  plates  ; 


FOSSIL    GANOIDS 


157 


Eurynotiis  (Fig.  159)  had  attained  a  great  depth  of  body 
and  prominent  dorsal  fin  ;  Cheirodus  (Fig.  160)  was  dis- 
tinctly flattened ;  Semionotus  (Fig.  161)  was  small,  with 


Fig.  160.  —  Cheirodus  granulosus,   Young,     x  \.     Coal   Measures,   Scotland. 
(After  TRAQUAIR.) 

elaborate  fin  conditions ;  Aspidorhynchus  (Fig.  162)  had  a 
remarkable  pointed  snout  and  a  reduced  number  of  body 


Fig .    161 .  —  Semionotus 
Keuper,  Stuttgart. 


,   Fraas.      X  }.     (From  ZlTTEL,   after  FRAAS.) 


plates  ;  Microdon  (Fig.  163),  flattened  like  Cheirodus,  had 

evolved  an  admirable  series  of  crushing  teeth  (-Pycnodont). 

And,  finally,  is  to  be  mentioned  Palaoniscus  (Fig.  164), 

a  form  whose  abundance,  numerous  species,  and  long  sur- 


158 


TELEOSTOMES 


viva!  (Palaeozoic-Mesozoic)  have  made  it  the  most  widely 
known   of   fossil   fishes.      Of    all   extinct    Ganoids   there 


Fig.  162. — Aspidorhynchus  acutirostris,  Agassiz.    X  f.    (After  ZlTTEL.)     Jura, 
Solenhofen. 

appears  to  attach  to  Palaeoniscus  the  greatest  morphological 
interest ;  on  the  one  hand,  it  seems  closely  akin  to  the 


^Fig.  163.  —  Microdon  wagneri,  Thiolliere.     X  \.     (From  ZlTTEL,  after  THIOL- 
LIERE.)     Jura,  Cerin. 


LIVING    GANOIDS 


159 


recent  gars,  and,  on  the  other,  even  as  evidently  to  the 
sturgeons  ;  of  all  fossil  kindred  of  these  living  forms,  it 
seems  most  nearly  in  the  ancestral  line. 


Fig.  164.  —  PalcBoniscus  macropomas,  Agassiz.  X  |.  (After  restoration  of 
TRAQUAIR.)  Upper  Permian. 

Ganoids  certainly  outrank  the  Crossopterygians  in  the 
number  and  variety  of  their  ancient  forms.  Their  few 
living  representatives  give  but  little  idea  of  the  importance 
of  the  group,  and  can  suggest  but  faintly  the  lines  of  its 
evolution. 

Living  Types 

The  recent  Ganoids  include  the  Gar-pike,  the  Sturgeons, 
and  Amia.  The  first  is  of  especial  interest  in  connecting 
the  group  most  closely  with  the  Crossopterygians,  the  last 
as  best  illustrating  the  intermediate  stage  between  the 
Ganoids  and  Teleosts. 

The  Gar-pike,  Lepidosteus  (Fig.  157),  resembles  Polyp- 
terus  in  many  characters  of  skeleton  and  dermal  defences. 
It  is  a  form  not  uncommon  in  the  fresh  waters  of  North 
America,  and  is  especially  abundant  in  the  Mississippi, 
Great  Lakes,  and  rivers  of  the  Southern  States.  In  South 
Carolina  the  writer  has  known  the  gar-pikes  to  occur  in 
such  numbers  that  they  would  fill  the  shad  nets,  and  for 
many  days  render  this  fishery  impracticable.  They  some- 
times attain  a  length  of  six  feet,  and  are  said  to  become 


!  60  TELE  OS  TOMES 

as  aggressive  as  sharks.  They  are  remarkably  tenacious 
of  life,  and  their  complete  armouring  of  dermal  plates 
renders  them  practically  invulnerable. 

In  development  Lepidosteus  has  apparently  more  prim- 
itive features  than  Acipenser  (v.,  p.  207 ;  also  Jour,  of 
Morph.  XI,  No.  i). 

Of  all  recent  Ganoids,  Lepidosteus  must  certainly  be 
looked  upon  as  retaining  most  perfectly  the  structural 
Characters  of  the  most  abundant  and  probably  the  most 
generalized  Palaeozoic  and  Mesozoic  forms.  Its  genus,  it 
is  true,  is  not  known  to  occur  earlier  than  the  Eocene,  but 
its  structures  —  scales,  fins,  labyrinthine  teeth  and  partially 
calcified  skeleton  —  are  known  to  have  been  possessed, 


Fig.  165.  —  The  sturgeon,  Acipenser  sturio,  L.  X  jV-  Streams  entering  North 
Atlantic.  (After  GOODE  in  U.  S.  F.  C.) 

even  in  their  details,  by  a  number  of  the  older  genera  and 
families. 

The  Sturgeons,  Acipenser >  Scaphirhynchus ,  Psephurus* 
Polyodon,  must  in  many  ways  be  looked  upon  as  of  a  highly 
adaptive  or  even  retrogressive  character.  There  is  strong 
evidence  that  in  their  descent  a  large  proportion,  and,  in- 
cases, all  of  their  dermal  armouring  has  been  lost,  and  that 
their  cusp-like  ancestral  teeth  have  either  disappeared  or 
are  retained  in  a  rudimentary  condition. 

The  interrelationships  of  the  four  surviving  forms  of 
sturgeons  have  not  as  yet  been  definitely  suggested  ;  transi- 
tional fossil  forms  have  thus  far  been  lacking,  and  the 
relative  importance  of  the  different  structures  in  the  recent 


THE  STURGEONS  l^l 

genera  cannot,  therefore,   be  determined  for  purpose  of 
comparison. 

The  genus  of  the  common  sturgeon,  Acipenser,  is  the 
most  completely  studied  of  the  recent  forms.  It  includes 
twenty  or  more  "species,"  varying  in  length  from  one 
(A.  brevirostris,  of  the  Eastern  United  States)  to  ten  yards 
(A.  huso,  of  Russia),  and  is  altogether  one  of  the  most  valu- 
able food-fishes  of  the  rivers,  lakes,  and  coasts  of  the  north- 
ern hemisphere.  It  is  a  sluggish,  bottom-feeding  fish, 
common  in  muddy  streams.  Its  broad  and  pointed  snout, 
sensory  barbels,  and  greatly  protractile  jaws  are  the  most 
striking  differences  from  the  Palaeoniscoid ;  its  dermal 


Fig.  165  A.  —  Chondrosteus  acipenseroides.     X  \.    From  Lias  of  Lyme  Regis. 
(Restoration  of  skeleton  after  SMITH  WOODWARD.) 

armouring  has  become  reduced  to  the  five  longitudinal 
bands  of  body  plates,*  but  is  more  perfect  in  the  tail 
region ;  its  skeleton  retains  an  entirely  cartilaginous  con- 
dition. In  its  larval  stage  conical  teeth  are  known  to  be 
present,  and  the  entire  series  of  dermal  plates  are  much 
larger  in  relative  size. 

A  figure  of  Chondrosteus,  a  Liassic  sturgeon,  may  here 

*  It  is  interesting  to  note  that  in  Palaeoniscoids  there  is  sometimes  a  notice- 
able tendency  for  the  five  rows  of  plates,  dorsal,  and  the  paired  lateral  and 
ventral,  to  increase  in  size,  suggesting  the  first  steps  in  the  origin  of  the  derm 
plates  of  Acipenser. 
M 


TELE  OS  TOMES 

parenthetically  (Fig.  165  A)  be  inserted ;  it  is  of  especial 
interest  as  suggesting  an  approximation  of  the  type  of  the 
modern  sturgeon  to  that  of  the  Palaeoniscoid ;  its  snout  is 
shorter  than  in  Acipenser ;  its  jaws  larger,  and  apparently 
less  protrusible ;  its  dermal  plates  of  the  head  region, 
including  the  branchiostegals,  are  clearly  of  the  ancient 
pattern,  and  the  fins,  fin  supports,  and  vertebral  characters, 


Fig.  166.  —  The  shovel-nose  sturgeon,  Scaphirhynchus  platyrhynchus  (Raf.), 
Gill.  X  \.  Mississippi  basin.  (After  GOODE  in  U.  S.  F.  C.) 

together  with  the  general  small  size  of  the  fish,  suggest 
intermediate  conditions. 

Of  the  remaining  sturgeons,  the  shovel-nose,  ScapJii- 
rhynchus  (Fig.  166),  of  the  Mississippi  and  of  Central  Asia, 
seems  to  possess  the  closest  relations  to  Acipenser; 
although  it  is  apparently  a  more  modified  form,  on  account 
of  its  elongate  body  shape  and  flattened  snout,  it  still 
retains  many  interesting  and  archaic  features.  Among 


Fig.  i66A. — Psephurus gladius,  Gun.  x  \.  Rivers  of  China.  (After  GUNTHER.) 

these  it  includes  the  most  complete  dermal  armouring  of 
recent  forms,  its  hinder  body  region  being  entirely  encased. 
Psephiirus  (Fig.  i66A),  of  the  Chinese  rivers,  and  Poly- 
odon,  or  Spatularia  (Fig.  166  B\  of  the  Mississippi,  are 
the  other  forms  of  living  sturgeons.  Their  greatly  elon- 
gate snouts,  giving  them  the  popular  names  of  Spoonbills, 
Paddle-fish,  Spear-fish,  are  among  the  most  remarkable 


STURGEONS  AND  AMIA 


163 


sensory  appendages  of  fishes.  They  have  been  but  little 
studied,  and  their  relations  to  Acipenser  have  never  been 
satisfactorily  determined.  They  have  certainly  many  feat- 


Fig.  i66B. — The  spoon-bill  sturgeon  or  paddle-fish,  Polyodon  spatula  (Walb.), 
J.  and  G.     X  |.    Ventral  and  side  view.    Mississippi  basin.     (After  GOODE.) 

ures  in  skeletal  parts,  fin  structures,  lateral  line  organs, 
jaws,  teeth,  which  can  only  be  looked  upon  as  of  primitive 
character ;  on  the  other  hand,  their  highly  specialized  ros- 
trum, degenerate  opercula,  and  want  of  dermal  amouring 
would  suggest  an  early  divergence  from  the  main  stem  of 
the  sturgeons.  To  the  writer,  Psephurus  seems  the  more 
generalized  of  these  peculiar  forms. 


Fig.  167.  —The  bowfin,  Amia  calva,  L.  X  \.  (After  GOODE  in  U.  S.  F.  C.) 
Central  and  Eastern  United  States. 

Amia  calva  (Fig.  167)  is  the  last  of  the  recent  Ganoids 
to  be  noted.  Its  distribution  corresponds  closely  with 
that  of  the  gar-pike ;  it  is  a  common  form,  worthless  as 


1 64 


TELEOSTOMES 


a  food-fish,  but  deemed  worthy  of  a  host  of  local  names, 
as :   Bowfin,  Grindle,  Dog-fish,  Mud-fish,  Sawyer,  Joseph 

Grindle,  Lawyer-fish.  Its 
interest,  as  already  sug- 
gested, is  in  its  close  kin- 
ship to  the  Teleosts  on 
the  one  hand,  and  to  the 
sturgeons  and  gars  on  the 
other.  Its  cycloidal  scales, 
its  fin  structure,  and  cal- 
cified skeleton  seemed  of 
so  modern  a  character, 
that  it  was  long  included 
among  the  members  of 
the  herring  group;  only 
after  a  closer  examination 
did  its  primitive  struct- 
ures become  apparent. 
It  is  one  of  the  few  Gan- 
oids which  possess  a  gular 
plate  (Fig.  i68,/#g-).  Like 
that  of  Lepidosteus,  its 
air-bladder  is  cellular,  and  of  respiratory  value  (Wilder). 


Fig.  168.  —  Amia.    Ventral  view  of  jaw 
region,      x  i.      (After   ZITTEL). 

brs.    Branchiostegal    rays.      h.    Cerato- 
hyal.  jug.  Jugular  plate,    md.  Mandible. 


Fig.  169. —  Caturus  furcatus.     x  J.     (From  SMITH  WOODWARD,  after  AGAS- 
SIZ.)     Lithographic  stone  (Upper  White  Jura),  Solenhofen. 

The  relations  of  Amia  become  of  especial  interest,  in 
view  of  the  number  and  range  of  its  fossil  kindred.     Its 


TELEOST-LIKE    GANOIDS 


I6S 


group  is  known  to  have  attained  its  prominence  at  a  later 
geological  time  than  the  other  Ganoids ;  it  is  doubtless 
derived,  more  or  less  directly,  from  the  main  ganoidean 
stem.  Three  of  the  more  typical  Mesozoic  forms  are 
shown  in  Figs.  169,  170,  171,  in  Caturus,  Leptolepis,  and 


Fig.  170. — Leptolepis  sprattiformis.  X  f .  (From  SMITH  WOODWARD.)  Lith- 
ographic stone,  Solenhofen. 

Megalurus.  To  these  amioid  forms  the  ancestry  of  the 
(majority  of  the)  Teleosts  is  reasonably  to  be  traced. 

A  general  scheme  of  the  phylogeny  of  the  Teleostomes 
is  suggested  on  the  adjoining  page  (Fig.  171  A). 

B.  Teleocephali  (Teleosts?)  This  group,  popularly  known 
as  that  of  the  bony  fishes,  or  Teleosts,  includes  as  great 
a  proportion  perhaps  as  95  per  cent  of  the  kinds  of  fishes 


Fig.  171.  —  Megalurus  elegant  is  simus,  Wagner. 
Solenhofen. 


X  |.     (After  ZlTTEL.)     Jura, 


living  at  the  present  time.  The  immense  number  of  their 
genera  and  species  is  doubtless  suggestive  of  the  form 
changes  which  occurred  during  the  flowering  periods  of 
the  sharks,  chimaeroids,  or  lung-fishes. 

Teleosts  have  diverged  most  widely  of  all  fishes  from 


1 66 


TELEOSTOMES 


what  seem  to  have  been  their  primitive  structural  condi- 
tions. Their  skeleton  has  become  highly  calcined,  its  ele- 
ments multiplying,  fusing,  and  specializing.  The  notochord 
has  practically  disappeared,  owing  to  the  complete  formation 
of  bony  vertebne.  The  derm  bones  of  the  head,  which  in 


ANCESTRAL 
TELEOSTOME 


(TABLE  IV) 


PALAEOZOIC 

PALAEONISCOID 


LEP.OOST'E'us'^siLUKo.D    I  p^^ME    \\\\\\\\      LopHOB**NCH 

POLYPTERUS  AM.A  MEACANTHOPTtRYS.AN  BYPATH 

Fig.  171  A.  —  The  Phylogeny  of  the  Teleostomes. 

the  ancestral  Ganoid  were  at  the  surface,  enamel-coated,* 
are  now  deep-seated  in  the  head,  resembling  true  cartilage 
bones ;  their  surfaces  are  usually  deeply  furrowed  or  ridged, 

*  The  enamel  of  Ganoid  plates  (ganoine)  appears  to  be  derived  from  the 
underlying  bony  tissue,  not  deposited  by  the  overlying  epidermis  (enamel 
organ) . 


EVOLUTION  OF  TELEOSTS 


I67 


and  their  character  is  often  squamous.  Scales  are  widely 
specialized,  thin,  horn-like,  ornate,  overlapping  their  outer 
margins,  their  inner  rims  set  deeply  but  loosely  in  dermal 
pockets  (Fig.  31).  Fins  are  dermal  structures,  their  ancient 
basal  supports  hardly  to  be  distinguished ;  the  primitive 
tail  structure  is  so  masked  by  clustered  and  fused  skeletal 
elements  that  its  heterocercy  is  scarcely  apparent.  In 
short,  the  most  widely  modified  conditions  can  be  shown 
to  exist  in  Teleosts  in  almost  every  structural  character, 
as  in  gills,  teeth,  opercula,  circulatory  and  urinogenital 
organs,  sensory  structures,  and  nervous  system.  They 
have  evidently  been  competing  keenly  in  the  struggle  for 
survival,  for  in  every  detail  of  form  or  structure  the  most 
varied  conditions  exist.  In  addition  to  these  structural 
adaptations  of  Teleosts,  changes  in  coloration  have  been 
rendered  possible  by  the  transparency  of  their  scales  ;  and 
in  their  different  families  these  changes  have  taken  place 
often  with  striking  results :  adaptive  coloration,  brilliant, 
dull,  mottled,  inconspicuous,  occurs  with  a  range  of  varia- 
tion which  is  not  surpassed  even  by  the  colours  of  birds. 

It  is  not  remarkable,  therefore,  that  members  of  the 
different  groups  of  Teleosts  should  often  parallel  each 
other  in  structural  likenesses,  when  placed  under  the  same 
environmental  conditions.  Each  organ,  in  fact,  rrtay  be- 
come a  centre  of  variation,  and  confuse  the  line  of  the 
descent  of  the  minor  groups ;  for  the  keenest  judgment 
cannot  select  of  all  these  varying  structures  those  which 
can  definitely  be  made  the  standards  of  general  comparison. 
Environment,  like  a  mould,  has  impressed  itself  upon 
forms  genetically  remote,  and  in  the  end  has  placed  them 
side  by  side,  apparently  closely  akin,  similar  in  form  and 
structure. 

A  striking  instance  of  changes  due  to  environment  is 


i68 


TELEOSTOMES 


well  known  in  the  case  of  Deep-sea  Fishes,  in  their  acquir- 
ing a  characteristic  shape  under  the  conditions  of  abyssal 
life.  The  head  region  of  these  forms  becomes  greatly 
exaggerated  in  size,  and  the  trunk  tapers  suddenly  away 
toward  the  tip  of  the  pointed  tail.  The  tissues  become 
extremely  modified,  soft,  porous,  delicate,  often  trans- 
parent ;  skeletal  parts  are  deficient  in  lime,  and  loosely 
articulated.  Many  organs  are  retained  in  curiously  unde- 
veloped or  aborted  conditions  ;  the  vertebral  axis  is  noto- 


Figs.  172-174.  —  Deep-sea  fishes.  (After  GUNTHER.)  172.  Paraliparis  bathy- 
bius.  640  fathoms.  173.  Bathyonus  compressus,  1400  fathoms.  174.  Notacanthus 
sexspinis.  1800  fathoms. 

chordal ;  gill  arches,  as  many  as  six  (?)  in  number,  may  open 
freely  to  the  surface,  never  enclosed  by  opercula ;  sensory 
canals  remain  as  open  grooves  as  in  the  most  generalized 
fishes ;  paired  fins  are  retained  either  in  an  undeveloped 
condition  or  are  not  produced  at  all.  Absence  of  light  has 
been  not  without  its  effects  ;  body  colours  are  usually  dark 
and  meaningless ;  while,  on  the  other  hand,  when  eyes  still 


DEEP-SEA    TELEOSTS  AND  FIERASFER 


169 


occur,  a  widely  modified  series  of  integumentary  phos- 
phorescent organs  are  often  evolved  as  lures  by  predatory 
forms.  It  is  evident,  in  the  case  of  deep-sea  fishes,  that 
the  simple  condition  of  their  structures  does  not  separate 
them  widely  in  point  of  descent  from  more  specially 
evolved  Teleosts.  Intermediate  forms,  occurring  in  shal- 
lower water,  often  connect  them  clearly  with  different,  and 
widely  distinct,  groups  of  bony  fishes.  In  this  way  the 


Fig.  175.  —  Fieras/er  acus,  Kaup.     X  |. 
cucumber  in  southern  waters. 


(After  EMERY.)     Commensal  of  sea- 


forms  which  are  shown  in  Figs.  172,  173,  174  are  severally 
connected  with  the  cottid,  the  cod  and  the  salmon,  al- 
though the  striking  similarity  of  their  outward  structures 
would  naturally  lead  one  to  regard  them  as  far  more 
intimately  related. 

Another  interesting  instance  of  the  modification  of  a 
fish's  form  by  its  living  conditions  has  often  been  noted  in 
the  case  of  Fierasfer  (Fig.  175).  This  small  Teleost  lives 
as  a  commensal  in  the  branchial  chamber  of  the  sea-cucum- 


TELEOSTOMES 

ber,  and  from  its  peculiar  life  habit  retains  permanently 
a  number  of  its  embryonic  characters ;  it  has  thus  its 
elongated  larval  form,  a  functional  pronephros,  a  noto- 
chordal  skeleton  and  immature  fin  conditions  (Emery, 
Ref.  p.  249). 

To  what  degree  the  structures  of  fishes  may  be  varied 
by  artificial  selection  is  an  interesting  question,  but  one 
that  has  as  yet  received  little  attention  even  from  those 
who  have  made  artificialization  an  especial  study.  In  the 
instance  of  the  Goldfish  it  is  well  known  how  wide  a 


Fig.  176.  —  Goldfish,  Carassius  auratus  ("Telescope"   variety).     X  i.     (After 

TXTTUT?!?    ~\  lotion 


GUNTHER.)     Japan. 

variation  has  been  produced  in  colour,  size,  and  proportions. 
Fin  structures  are  elaborately  developed,  long,  drooping, 
lace-like,  often  to  a  degree  which  must  render  progression 
both  slow  and  difficult.  Even  the  eyes  have  been  made 
to  become  large  and  protruding  (Telescope-fish,  Fig.  176). 
In  carp  the  variation  in  scale  character,  due  to  artificializa- 
tion, is  also  to  be  mentioned.  It  is  natural,  perhaps,  that 
artificial  selection  has  been  most  successfully  practised 


CA  TFISHES 


I/I 


among  these  forms  which  compete  most  actively  for 
survival. 

To  conclude  the  present  chapter,  several  forms  of  Tele- 
osts  may  be  briefly  discussed  as  especially  characteristic 
of  the  group,  namely  the  catfish,  Mormyms,  eel,  perch, 
cod,  flodnder,  porcupine-fish,  sea-horse. 

TJ*e  catfish,  representing  the  Siluroids,  has,  as  already 
noted,  many  structural  affinities  to  the  sturgeon,  and  is, 
perhaps,  a  direct  descendant  of  some  early  type  of  Mesozoic 
Palaeoniscoid.  It  is  a  representative  of  a  large  and  wide- 
spread family,  usually  of  river  fishes.  Its  habits  are  slug- 


Fig.  177. — The  bull-head  (catfish),  Amiurus  melas  (Raf.),  Jord.  and  Cope- 
land.     X  £.     (After  GOODE  in  U.  S.  F.  C.)     Eastern  North  America. 

gish  and  mud-loving.  Its  trunk  is  heavy,  rounded,  and 
without  Teleostean  scales ;  its  broad  mouth  margin  is  pro- 
vided with  barbels  ;  the  fin  rays  of  its  dorsal  and  pectoral 
fins  /fuse  into  a  stout,  serrate,  erectile  spine.  In  North 
American  forms  armouring  derm  plates  are  developed 
only  on  the  head  roof  (Fig.  177).  Closely  akin  to  these 
are  the  Asiatic  genera,  and  the  single  European  species, 
Silunis  glanis,  the  gigantic  We  Is  of  the  Danube.  The 
Nile  is  of  interest  if  only  for  its  forms  of  catfish  to 
parallel  the  shapes  and  structures  of  the  recent  Teleosts. 


172 


TELEOSTOMES 


In  South  America  the  catfish  is  a  regnant  type,  and  is 
remarkable  for  the  variety  as  well  as  for  the  number  and 
size  of  its  forms.  Many,  completely  armoured  (Fig.  178), 
are  strongly  suggestive  of  Ganoids.  Their  armouring  is 


Fig.  178.  —  South    American   Siluroid,     Callichthys    armatus.      X  i. 
GUNTHER.)     Upper  Amazon. 


(After 


metameral  and  archaic,  their  sensory  canals  primitive  in 
structure  and  arrangement. 

Mormyrus,  like  the  catfish,  appears  to  have  long  been 
divergent  from  the  main  stem  of  the  Teleosts.     Its  species 


Fig.  179.  —  Mormyrus  oxyrhynchus.     x  |.     (After  GUNTHER.)     Nile. 


are  restricted  to  the  Nile,  one  —  the  long-nosed  M.  oxyrhyn- 
chus (Fig.  179)  —  figuring  prominently  in  Egyptian  myth. 
In  many  of  its  structures  it  is  archaic,  as  in  axial  skeleton, 
fins,  dermal  characters,  sensory  canals  ;  in  others,  e.g.  hear- 


EEL-LIKE  FORMS 


173 


ing  organ,  it  is  most  highly  specialized.     Its  group  is  an 
interesting  one,  and  has  been  but  little  studied. 

The  Eel  (Fig.  180)  might  well  be  taken  as  one  of  the 


Fig.  180.  —  The  eel,  Anguilla  vulgaris,  Turton.     X  \.     (After  GOODE  in  U.  S. 
F.  C.)     Europe,  South  Asia,  North  Africa,  North  America. 

fish  forms  evolved  by  special  environment.  Living  in  soft 
river  bottoms,  a  serpent-like  movement  in  progression  has 
gradually  been  acquired ;  its  form  has,  therefore,  become 
elongated  and  rounded,  and  the  internal  structures  corre- 
spondingly modified.  Fin  structures  have  accordingly  been 


V-' 

Fig.  181.  — The  perch,  Perca  americana  (=Jluviatilis?),  Schrank.  X  k.  (After 
GOODE  in  U.  S.  F.  C.) 

metamorphosed,  ventral  fins  lost,  tail  degenerated,  and  a 
continuous  dorsal  and  ventral  secondarily  evolved ;  scales 
have  become  reduced  in  size,  supplanted  by  mucous  layers. 


TELE  OS  TOMES 

Similarity  in  eel-like  form,  e.g.  as  of  Murcena,  is  not   in 
itself  indicative  of  direct  kinship.     (Apodes.) 

The  Perch  (Fig.  181)  has  long  been  taken  as  a  repre- 
sentative Teleost.  Perfect  in  its  "lines,"  its  compact, 
wedge-like  shape  cleaves  the  water  by  vigorous  thrusts  of 
a  strong  broad  caudal ;  its  fins  are  stout,  supported  by 
spinous  rays ;  its  dermal  armouring  light,  smooth,  and  flex- 
ible ;  its  colour  is  brilliant  under  its  transparent  scales. 
So  adapted  is  it  to  its  environment  that  its  organ  of  static 
equilibrium,  the  air-bladder,  has  lost  its  valvular  connec- 
tion with  the  gullet.  Of  existing  fishes  about  one-half  are 
essentially  percoid.  (Acanthopterygii.} 


Fig.  182.  —  The  codfish,  Gadus  morrhua,  L.     X  &.     (After  GoODE  in  U.  S. 
F.  C.)     North  Atlantic. 

The  Cod  (Fig.  182)  is  scarcely  less  important  as  a  repre- 
sentative Teleost.  Its  structural  differences  may  perhaps 
represent  the  result  of  a  competition  less  active  than  that 
of  the  perch  in  the  struggle  for  survival.  Heavy  in  body, 
its  sluggish  form  has  become  blunted  and  rounded;  its 
fins  are  depressed,  their  rays  soft  and  yielding;  its  scales 
are  reduced  in  size,  colours  less  vivid;  its  swim-bladder 
loses  its  connection  with  the  gullet.  As  many,  perhaps, 
as  one  quarter  of  the  existing  genera  of  fishes  may  be 
assigned  to  this  type.  (Anacant/iini.) 

The  Flounder  (Fig.  183)  should  be  mentioned  as  a  singu- 


FLOUNDERS  AND  PORCUPINE-FISHES  ^5 

lar  instance  of  environmental  evolution,  its  flattened  body 
adapting  itself  both  in  shape  and  colour  to  its  bottom 
living.  Its  entire  side,  —  not  the  ventral  region,  as  in  the 
rays,  —  is  flattened  to  the  bottom.  The  unpaired  fins  now 
become  of  especial  value ;  they  increase  in  size,  and  their 
undulatory  movements  enable  the  fish  to  swim  rapidly  yet 
retain  its  one-sided  position ;  ventral  fins  become  useless, 
and  degenerate.  The  further  adaptations  of  the  flat  fish 
include  its  pigmentation  only  on  the  upper  or  light-exposed 
side,  and  the  rotation  of  the  eye  fro'm  the  blind  to  the  upper 


Fig.  183. — The  winter  flounder,  Pseudopleuronectes  americanus  (Walb.),  Gill. 
X  \.  (After  GOODE  in  U.  S.  F.  C.)  North  Atlantic. 

side,  —  in  this  giving  one  of  the  most  remarkable  cases  of 
adaptation  known  among  vertebrates.     (Heterosomata.} 

The  Porcupine-fish  (Fig.  184)  may  be  referred  to  as 
another  singular  result  of  environmental  evolution.  Its 
globular  and  inflatable  form  bespeaks  slowness  of  motion 
and  helplessness  if  exposed  to  changes  of  temperature 
or  current.  Its  fins  are  reduced  and  feeble,  suited,  how- 
ever, to  its  tranquil  habitat ;  its  fused  jaws,  parrot-like, 
show  in  how  special  a  way  its  food  is  best  secured.  It 
has  evolved  a  protective  casing  of  enormous  needle-like 
scales,  whose  shape  parallels  that  of  the  derm  denticles 


TELEOSTOMES 


of  the  shark.  As  a  somewhat  transition  form  to  the  more 
usual  conditions  of  the  Teleost,  the  Rabbit-fish  has  been 
figured  (Fig.  184^).  (Plectognathi.) 


Fig.  184.  —  The  porcupine-fish,  Chilomycterus geometricus  (Schn.),  Kaup.     x 
(After  GOODE  in  U.  S.  F.  C.  report.)     Warmer  Atlantic. 


Fig.  184  A.  — The  rabbit-fish,  Lagocephalus  Iczvigatus  (L.),  Gill.  X  \.  (After 
GOODE  in  U.  S.  F.  C.)  Northeast  Atlantic. 

A  final,  perhaps  the  most  bizarre,  instance  of  adapta- 
tion among  Teleosts  is  that  of  the  Sea-horse  (Fig.  185). 
In  spite  of  its  many  structural  oddities,  its  genetic  kin- 
ship with  the  Sticklebacks  (Hemibranchiates)  cannot  be 
doubted.  Yet  to  have  attained  its  present  form  its  evolu- 
tion must  have  been  carried  along  a  widely  divergent  path. 
It  may,  in  the  first  place,  have  fused  the  lines  of  its  meta- 
meral  scales,  dividing  off  the  surface  of  its  elongate  body 


SEA-HORSE  AND  PIPE-FISH 


177 


in  sharp-edged  rectangles,  whose  corners  became  produced 
as  spines.  At  this  stage  of  evolution  its  appearance  might 
well  be  represented  by  (Fig.  185  A)  the  kindred  Pipe-fish. 
To  secure  more  perfect  anchorage  in  its  algous  feeding- 
ground,  its  body  terminal  must  now  have  discarded  its  fin 
membranes  and  become  prehensile,  —  probably  the  most 
remarkable  adaptation  in  the 
entire  class  of  fishes,  since  it 
causes  metameral  organs  to 
change  the  plane  in  which  they 
function  from  a  horizontal  to  a 
vertical  one.  As  a  probable  de- 
velopment of  prehensilism,  three 
changes  may  next  have  been 
wrought :  the  flexure  of  the  neck 
region,  the  thickening  of  the 
trunk,  and  the  metamorphosis 
of  the  fins.  The  first  change 
may  have  been  brought  about 
by  the  normal  position  of  the 
fish's  axis  becoming,  as  is  well 
known,  vertical ;  the  head  then 
assumes  its  normal  horizontal 
plane  and  thus  parallels  mildly 
the  cranial  flexure  of  higher  ani- 
mals. The  enlargement  of  the 

Fig.  185.  —  The  sea-horse,  Hip- 

trunk  region  is  evidently  of  static  pocampus  heptagonus,   Raf.     x  j. 

i  T-i.         i<.        *.-  c  ^i-  (After  GOODE  in  U.  S.  F.  C.)    East 

value.    The  alteration  of  the  po-  ^oast  of  North  America> 
sition,  size,  and  degree  of  move- 
ment of  the  pectoral  fins,  the  loss  of  the  ventrals  and  the 
changed  function,  now  one  of   propulsion,  of  the  dorsal, 
appear  clearly  the  result  of  the  altered  plane  of  the  fish's 
motion.     Further  structural  changes  might  with  interest 


TEtEOSTOMES 


be  followed,  as  in  characters  of  viscera,  gills,  and  endo- 
skeleton.     In  its  life  habits  mimicry  is  strongly  evinced ; 


Fig.  185  A.  —  The  pipe-fish,  Syngnathus  acus  J,  L.,  showing  abdominal  pouch. 
X  i.     (After  GtJNTHER.)     Coasts  of  Europe  and  Africa. 

the  well-known  genus  Phyllopteryx,  whose  entire  body 
surface  develops  pigmented  appendages,  is  with  difficulty 
to  be  distinguished  from  a  rough-shaped  seaweed.  (LopJw- 
Itranchii.} 


• 


VIII 
THE   DEVELOPMENT   OF    FISHES 

THE  groups  of  fishes  have  hitherto  been  contrasted 
in  the  structures  of  their  living  and  fossil  forms.  They 
should  next  be  reviewed  in  the  light  of  their  mode  of 
development ;  for  the  developmental  stages  of  the  Shark, 
Lung-fish,  or  Teleostome  might  be  expected,  according 
to  time-honoured  belief,  to  furnish  important  evidence 
as  to  their  descent  and  interrelationships.  The  younger 
stages  of  the  various  forms  of  fishes  should  thus  suggest 
their  ancestral  characters :  the  developing  Teleost  should 
approach  the  Ganoid ;  the  Lung-fish  and  the  Ganoid 
should  resemble  their  supposed  elasmobranchian  ancestor. 

But  the  embryology  of  fishes  is  in  this  regard  very 
inconclusive,  if  at  present  in  any  important  way  sugges- 
tive. The  majority  of  the  forms,  including  some  of  the 
most  important,  are  developmentally  unknown ;  yet  suffi- 
cient is  known  of  the  representative  members  of  the 
groups  to  show  the  most  perplexing  characters.  On  the 
one  hand,  the  developmental  processes  of  forms  which  are 
regarded  by  the  morphologist  as  closely  akin  seem  often 
widely  distinct;  and,  on  the  other  hand,  the  fishes  which 
should,  a  priori,  exhibit  an  archaic  mode  of  development 
actually  present  complex  processes  of  early  growth  which 
can  only  be  interpreted  as  highly  specialized.  In  fact, 
there  are  far  greater  differences  in  the  developmental  plans 

179 


DEVELOPMENT   OF  FISHES 

of  the  closely  related  Ganoid  and  Teleost,  than  in  those  of 
a  Reptile  and  a  Bird  ;  and  even  among  the  members  of  the 
single  group,  Teleosts,  there  are  more  striking  embryolog- 
ical  differences  than  those  between  Reptiles  and  Mammals. 
Adaptive  characters  have  entered  so  largely  into  the  plan 
of  the  development  of  fishes  that  they  obscure  many  of 
the  features  which  might  otherwise  be  made  of  value  for 
comparison.  And  until  the  controversies  regarding  some 
of  the  most  fundamental  principles  in  embryology  —  e.g. 
the  importance  of  the  loss  or  gain  of  food  yolk  —  shall  be 
decided,  it  seems  impracticable  to  use  the  plan  of  develop- 
ment as  in  any  strict  sense  a  guide  in  phylogeny. 

It  is,  accordingly,  rather  with  the  view  of  contrast- 
ing the  groups  of  fishes,  whose  external  features  have 
hitherto  been  compared,  that  the  present  chapter  seems 
of  especial  importance.  They  may  briefly  be  reviewed  in 
their  (A)  spawning  habits,  (B)  the  mode  of  fertilization 
of  their  eggs,  (C)  their  embryonic,  and  (D)  larval  de- 
velopment. 

A.    EGGS   AND   BREEDING   HABITS 

The  eggs  of  typical  fishes  in  Figs.  186-199,  illustrate 
how  wide  a  range  occurs  in  their  shapes  and  sizes.  All 
are  of  about  actual  size,  except  Figs.  189-191,  which  have 
been  reduced  about  two-thirds.  From  the  figures  the 
character  of  the  egg  membranes  may  also  be  contrasted. 

Among  Cyclostomes,  which  are  usually  looked  upon 
as  of  close  genetic  kinship,  there  appears  a  striking  dif- 
ference in  the  characters  of  the  eggs.  Those  of  Bdello- 
stoma  and  Myxine  (Figs.  186,  187)  are  large  and  bluntly 
spindle-shaped,  encased  in  a  horn-like  capsule  ;  those,  on 
the  other  hand,  of  Petromyzon  are  minute,  spherical,  and 
enclosed  in  delicate  and  jelly-like  membranes  (Fig.  188). 


Figs.  186-199.  —  Eggs  and  egg  cases  of  fishes.  All  of  about  actual  size  except  189-91 ; 
these  have  been  reduced  about  two-thirds.  186.  Bdellostoma:  germ  disc  (?)  at  upper  pole 
and  in  186  A  terminal  hook  processes  and  micropyle.  (After  AYERS.)  187.  Myxine.  (After 
STEENSTRUP.)  187  A.  Terminal  process.  188.  'Petromyzon  marinus.  189.  Shark,  Scyllium. 
(After  GtNTHER.)  189  A.  Skate,  Raja.  190.  Port  Jackson  shark,  Cestracion.  (After 
GUNTHER.)  191.  Chimaeroid,  Callorhynchus.  (After  GiJNTHER.)  192.  Lung-fish,  Ceratodus. 
(After  SEMON.)  193.  Ganoid,  Lepidosteus.  194.  Ganoid,  Acipenser.  195.  Siluroid,  Arius, 
showing  larva.  (After  GiJNTHER.)  196.  Teleosts  :  sea-bass,  Serranus,  and  197.  shad,  Alosa. 
198.  Blenny,  Blennius,  showing  attached  egg  capsules.  199.  Enlarged  Blennius  (after 
GuiTEL) ,  showing  mode  of  attachment  of  capsule. 

181 


j32  DEVELOPMENT   OF  FISHES 

The  eggs  of  Myxinoids  are  probably  deposited  at  a 
single  time  ;  at  first  extruded  by  pressure  of  the  body 
wall ;  then  drawn  out  string-like,  one  egg  following 
another,  attached  by  hooked  and  thread-like  processes 
(Figs.  186^4,  187  A).  Little  is  known,  however,  of  the 
actual  breeding  habits  of  Myxinoids,  either  as  to  locality, 
mode,  or  season ;  individuals  of  Myxine  and  Bdellostoma 
with  ripe  spawn  have  never  been  taken  even  in  the 
most  favourable  regions.  It  is  supposed  that  their  spawn- 
ing does  not  occur  in  the  immediate  neighbourhood  of 
the  shore,  since  detached  eggs  have  been  dredged  in  the 
deeper  water.  Their  breeding  time  is  probably  in  the 
early  spring,  although  possibly  intermittent  spawning 
takes  place.  In  Myxine,  according  to  Putnam,*  the  bulk 
of  the  eggs  may  be  deposited  as  late  as  the  beginning  of 
winter. 

The  spawning  habits  of  Petromyzon,  on  the  other  hand, 
have  been  especially  favourable  for  observation.  The  eggs 
are  deposited  in  shallow  and  clear  water  and  the  move- 
ments of  the  fish  may  readily  be  followed.  In  the  small 
stream  at  Princeton,!  for  example,  the  lampreys  make  their 
appearance  about  the  middle  of  May  and  remain  on  the 
spawning  grounds  two  or  three  weeks.  Their  "nests" 
are  seen  scattered  thickly  on  the  gravelly  shoals,  often  but 
a  few  feet  apart.  Each  will  be  occupied  by  several  males 
and  a  single  female,  the  latter  conspicuous  on  account  of 
greater  size.  When  spawning,  the  lampreys  press  together 
and  cause  a  flurry  in  the  water  at  the  moment  when  the 
eggs  and  milt  are  emitted.  This  portion  of  eggs  will  now 

*  As  observed  at  Grand  Menan.     Pro.  Bost.  Soc.  Nat.  Hist.     Feb.  '74. 

t  Professor  McClure  and  Dr.  O.  S.  Strong  have  here  repeatedly  observed 
the  spawning  lampreys;  it  is  to  their  account  that  the  writer  is  here  indebted. 
Compare,  also,  the  excellent  account  given  recently  by  Professor  Gage. 
Ref.  p.  234. 


EGGS   OF  ELASMOBRANCHS 


183 


be  covered  with  a  thin  layer  of  sand  or  gravel,  —  the 
spawners  always  returning  to  the  same  nest,  —  and  a  sec- 
ond, third,  and  more  tiers  of  eggs  will  be  added.  When 
the  eggs  have  finally  been  deposited,  the  nest  is  fortified 
by  a  dome-like  mass  of  pebbles  and  stones,  which  the  lam- 
preys carefully  drag  to  the  spot.  The  nest  is  thus  marked 
out  as  well  as  protected,  and  is  said  to  be  made  of  partial 
use  during  the  following  season.  The  hatching  of  the 
eggs  takes  place  within  about  a  fortnight. 

The  eggs  which  Sharks  and  Rays  deposit  are  usually 
enclosed  in  a  stout,  horn-like  capsule ;  this  is  in  general  of 
oblong  or  rectangular  outline,  its  surface  smooth  or  ridged ; 
the  case  of  the  egg  of  Scyllium  (Fig.  189),  shows  thread- 
like terminal  processes,  while  these  in  the  ray  (Fig.  189^) 
are  stout  and  spine-like.  A  great  variation  may  exist  in 
the  size  of  the  egg  and  in  the  character  of  its  envelopes 
among  the  different  groups  of  Elasmobranchs.  The  egg 
of  the  Port  Jacksqn  shark,  Cestracion  (Fig.  190),  is  of  enor- 
mous size  and  possesses  an  extremely  thick,  spiral-rimmed, 
pear-shaped  capsule  ;  that  of  the  Greenland  shark,  L&mar- 
gus,  is  said  to  be  spherical  and  relatively  small,  and  to  be 
deposited  unprotected  by  capsule. 

The  breeding  habits  of  Elasmobranchs  are  but  imper- 
fectly known.  With  the  exception,  perhaps,  of  Laemargus, 
the  sexes  copulate.*  The  clasping  appendages  of  the  male 
are  inserted  either  singly  or  together  into  the  cloaca  and 
oviduct  of  the  female,  and  the  eggs  appear  to  be  fertilized 
in  the  uppermost  portion  of  the  oviduct.  The  egg  then 
becomes  surrounded  by  a  glairy  albuminous  envelope,  and 
thereafter  by  the  secretion  of  the  oviducal  gland,  which  in 
the  lower  oviduct  hardens  into  the  horny  capsule.  The 

*  The  copulation  of  sharks  has  been  but  rarely  observed  (c.g.  by  Bolau  in 
Hamburg ;  cf.  Ref.  on  p.  241). 


1 84 


DEVELOPMENT   OF  FISHES 


majority  of  sharks  and  rays  are  viviparous ;  the  eggs  are 
retained  in  the  lowermost  portion  of  the  oviduct  (uterus) 
and  the  embryo  establishes  a  "placental"  circulation,  the 
vascular  yolk  sac  becoming  adherent  to  the  walls  of  the 
uterus.  Other  sharks  deposit  their  eggs,  and  their  mode 
of  oviposition  has  been  observed.  The  egg  (Fig.  189), 
when  slightly  protruded  from  the  cloaca,  is  rubbed  against 
brush-like  objects,  and  when  its  terminal  processes  become 
finally  entangled,  the  egg  is  withdrawn.  The  processes  of 
the  egg  case  which  leave  the  body  last,  the  longer  ones, 
are  often  greatly  straightened  out  when  the  egg  is  depos- 
ited ;  subsequently  their  elastic  character  causes  them 
to  curl  tightly,  and  often  to  secure  a  firm  attachment 
to  neighbouring  objects.  The  eggs  of  oviparous  skates 
(Fig.  189  A)  are  said  to  be  deposited  on  sand  flats  near 
the  mark  of  low  water.  Mr.  Vinal  N.  Edwards  of  Wood's 
Holl,  Massachusetts,  believes  that  they  are  implanted  ver- 
tically in  the  sand,  and,  from  the  occurrence  of  "beds" 
of  skate  eggs,  that  the  fishes  are  singularly  local  in  their 
places  of  spawning.  Eggs  of  Elasmobranchs*  are  often 
many  months  in  hatching ;  the  young  fish  finally  escapes 
through  a  slit  at  the  end  of  the  egg  case. 

Nothing  is  known  definitely  of  the  breeding  habits  of 
Chimaeroids.  The  mode  of  copulation  of  the  sexes  is 
doubtless  similar  to  that  of  sharks.  Their  clasping  organs 
are  highly  specialized  sperm  ducts,  and  the  hook-bearing 
organs  at  the  anterior  margin  of  the  ventral  fin,  and  on 
the  forehead  of  the  male,  function  in  all  probability  in 
retaining  the  female.  The  forehead  spine  could  certainly 
prove  of  such  service  if  the  position  of  the  fishes  during 
mating  was  at  all  similar  to  that  figured  for  Scyllium  by 

*  In  the  case  of  Scyllium  the  eggs  are  deposited  about  six  days  after  they 
have  been  fertilized ;  they  then  hatch  in  from  200  to  275  days. 


EGGS   OF  FISHES 


I85 


Bolau.*  The  egg  case  of  Callorhynchus  (Fig.  191)  is 
essentially  shark-like ;  it  is  of  spindle-shaped  outline,  and 
its  broad,  fringing  margin  gives  it  an  almost  seaweed-like 
appearance.  The  egg  is  believed  to  be  deposited  in  deep 
water. 

The  spawning  of  but  one  of  the  three  existing  Lung- 
fishes  has  been  recorded.  Ceratodus,  according  to  Semon, 
has  a  spawning  season  extending  over  several  months ;  it 
deposits  its  eggs  in  shallow  water,  scattering  them  broad- 
cast. The  female  fish  is  attended  by  several  males,  and 
the  emission  of  eggs  and  milt  appears  to  be  simultaneous. 
The  egg  (Fig.  192)  lacks  a  horny  capsule,  but  is  amply 
protected  by  a  thick,  jelly-like  hull.  It  hatches  during  the 
second  week. 

Eggs  of  Ganoids  are  shown  in  Figs.  193,  194.  They 
are  encased  in  a  jelly-like  envelope,  especially  viscid  in  the 
case  of  sturgeon.  When  deposited,  they  speedily  adhere 
to  whatever  they  touch,  and  often  remain  attached  until 
the  time  of  hatching.  The  spawning  grounds  are  in 
shallow  water ;  the  fish  occur  in  numbers  during  a  few 
days  of  May  and  June,  each  female  attended  by  several 
males  :  ova  and  milt  are  emitted  simultaneously,  at  short 
intervals.  The  eggs  develop  rapidly,  hatching  in  about  a 
week. 

The  eggs  of  Teleosts  present  the  utmost  variety  in 
number,  form,  membranes,  and  mode  of  deposition.  In 
some  forms  (Embiotocids,  Blenniids,  Cyprinodonts)  they 
may  even  develop  within  the  ovarian  tissue,  establishing 
there  a  "placental"  circulation.  They  have  been  fertilized 
within  the  fish,  the  anal  fin  spine  of  the  male  having  in 
some  cases  been  metamorphosed  into  a  copulatory  organ. 
The  eggs  of  Siluroids  (Fig.  195)  are  generally  of  large  size, 

*V.  Ref.  p.  241. 


I $6  DEVELOPMENT   OF  FISHES 

and  somewhat  adhesive;  they  are  deposited  in  "nests,"  i.e. 
bowl-like  depressions,  and  are  attended  by  the  male  fish.* 
Other  adhesive  eggs  are  those  of  carp,  Ckristiceps,  Batra- 
chus.  Eggs  of  Salmonids  are  deposited  loosely  in  "  nests  " 
on  a  clean,  gravelly  bottom;  their  membranes  are  thick 
and  parchment-like.  On  the  other  hand,  the  majority  of 
pelagic  fishes  produce  eggs  which  float  (Figs.  196,  197) ; 
of  these  the  membranes  are  extremely  hygroscopic  and 
transparent,  and  an  oil  globule,  located  in  the  yolk  region 
of  the  egg,  serves  to  diminish  its  specific  gravity.  The 
egg  membranes  of  a  number  of  Teleosts,  e.g.  Blennies 
(Fig.  199),  appear  essentially  shark-like ;  a  horn-like  cap- 
sule is  evolved,  whose  terminal  processes  afford  it  a  firm 
attachment.  Aberrant  modes  of  oviposition  are  not  lack- 
ing ;  the  South  American  Siluroid,  Aspredo,  as  is  well 
known,  carries  its  eggs  attached  to  its  ventral  surface ;  the 
pipe-fishes  and  sea-horses,  Siphostoma,  Solenostoma,  Hip- 
pocampus, have  specialized  a  pouch-like  fold  of  the  abdo- 
men and  of  the  ventral  fins,  which  serves  to  retain  the 
eggs  and  larvae.  It  is  curious  to  note  that  this  remark- 
able condition  occurs  only  in  the  male. 

The  breeding  habits  of  Teleosts  are  in  general  like  those 
of  Ganoids ;  their  spawning  season  is  usually  during  the 
spring  and  summer,  but  is  seldom  of  very  brief  duration. 
The  hatching  of  the  eggs  depends  largely  upon  water 
temperature,  and  may  vary  from  a  few  days  to  several 
months  (Salmo). 

B.   THE   FERTILIZATION   PHENOMENA 

The  processes  of  the  maturation  and  fertilization  of 
the  egg  have  as  yet  shown  but  minor  differences  in  the 

*  In  several  genera  they  are  carried  about  in  the  gill  chamber  of  the  male, 
thus  ensuring  aeration. 


EARLY  DEVELOPMENT 


I87 


groups  of  fishes.  In  the  forms  which  have  thus  far  been 
studied  *  there  have  been  few  noteworthy  variations  from 
what  appear  the  normal  conditions  of  vertebrates.  The 
sperm  usually  gains  admission  to  the  egg  through  a  micro- 
pyle  in  the  egg  membranes  which  becomes  formed  imme- 
diately after  the  extrusion  of  the  polar  bodies.  A  sperm 
cell,  invariably  a  single  one,  participates  in  the  actual 
fertilization.  This  may  occur  directly  by  the  formation  of 
a  single  male  pronucleus,  as  e.g.  in  Petromyzon,  Teleosts ; 
while  in  the  sharks,  on  the  other  hand,  Riickert  describes 
a  multiple  fertilization  (polyspermy),  where  many  male 
pronucleif  are  formed,  the  one  nearest  in  position  fusing 
subsequently  with  the  female  pronucleus.  An  inter- 
mediate condition  seems  to  be  retained  in  the  sturgeon, 
where  several  (six  to  nine)  micropyles  have  been  noted, 
although  but  a  single  one  occurs  in  the  kindred  Ganoid, 
Lepidosteus  (Mark,  Ref.  p.  249). 

C.  THE  EMBRYONIC  DEVELOPMENT 

When  the  egg  of  a  fish  is  deposited,  it  contains  but  the 
elements  of  a  single  cell.  Its  size  and  its  enveloping 
membranes  may  vary  widely,  but  its  constituents  are  con- 
stant, —  cytoplasm  and  nucleus.  The  size  of  the  egg  in 
different  fishes  varies  with  the  amount  of  food  material, 
or  yolk,  stored  away  in  its  cytoplasm ;  the  enormous  egg 
of  the  shark  differs  from  the  minute  egg  of  the  lamprey 
strikingly  in  this  regard.  But  even  in  the  minute  lamprey 
egg  there  is  a  certain  amount  of  yolk  material  present. 

In  every  egg  there  can  usually  be  distinguished  at  sight 

*  Lamprey  by  Kupffer  and  Bohm,  and  Calberla  ;  Sharks  by  Ruckert  ;  Te- 
leostomes  by  Hoffman,  Agassiz  and  Whitman,  Kupffer,  Bohm,  and  others. 

t  These  appear  later  to  undergo  karyokinesis,  and  are  thereafter  to  be 
regarded  as  supplemental  merocytes  (p.  195). 


DEVELOPMENT  OF  FISHES 

an  upper  and  a  lower  zone  :  the  latter  rich  orange  in  colour, 
caused  by  the  settling  of  the  heavier  yolk  material ;  the 
former  lighter  in  colour,  containing  the  nucleus  of  the  egg, 
and  originating  the  growth  processes. 

The  less  the  amount  of  yolk  in  the  lower,  or  vegetative, 
region,  the  smaller  is  naturally  the  egg,  and  the  more 
obscure  becomes  the  limit  of  the  upper  zone,  or  germ,  or 
animal  pole,  as  it  is  indifferently  called.  In  the  yolk- 
filled  egg  of  the  shark,  on  the  other  hand,  the  upper  zone 
becomes  reduced  to  a  mere  "germ  disc"  on  the  surface  of 
the  egg  (Fig.  216,  GD).  If  but  little  yolk  is  present,  the 
early  growth  processes,  i.e.  the  splitting  of  the  germ  cell, 
or  egg,  into  many  cells,  or  blastomeres,  to  give  rise  to  the 
embryo,  affect  the  entire  egg.  If,  however,  much  %  yolk  is 
present,  the  cells  at  first  multiply  only  at  the  animal  pole, 
and  the  yolk-filled  region,  remaining  unsegmented,  fur- 
nishes the  nutriment  for  the  cell  growth  above. 

In  the  present  outline  of  the  development  of  fishes, 
the  following  types  are  reviewed  :  — 

I.  Petromyzon  ;  II.  Shark  ;  III.  Lung-fish  ;  IV.  Ganoid  ; 
V.  Teleost. 

I.    The  Development  of  Petromyzon 

The  egg  of  Petromyzon  is  of  small  size  (Fig.  188),  and 
is  poorly  provided  with  yolk  material ;  in  surface  view  one 
can  only  distinguish  the  germinal  from  the  yolk  region  by 
its  slightly  lighter  colour.  In  the  side  view  of  the  egg  of 
Fig.  200,  the  beginning  of  the  first  cleavage  plane  is  seen ; 
a  vertical  plane,  passing  through  the  egg,  completes  the 
stage  of  the  two  blastomeres  of  Fig.  201.  The  nuclei  were 
at  first  close  to  the  upper,  or  animal,  pole,  but  they  shortly 
take  their  position  somewhat  above  the  plane  of  the  egg's 
equator.  A  second  cleavage  plane  is  again  vertical,  ap- 


FIG.  200 


201 


202 


EC 


204 


EN 


Figs.  200-215.  —  Development  of  lamprey,  Petromyzon  planeri.  Figs.  200-204,  208-212 
X  18,  others  X  about  30.  200,  201.  First  cleavage,  beginning  and  concluded.  202.  Third 
cleavage.  203.  Fourth  cleavage,  in  section,  showing  beginning  of  segmentation  cavity.  204, 
205.  Early  and  late  blastulae,  in  section.  206,  207.  Early  and  late  gastrulae,  in  section.  208, 
210,  212.  Early  embryos  showing  growth  of  head  end.  209,  211.  Sagittal  sections  of  early 
embryos  showing  differentiation  of  organs.  213,  214.  Transverse  sections  of  early  embryos. 
215.  Sagittal  section  of  newly  hatched  larva,  Ammocostes.  (Figs.  211,  215,  after  GOETTE,  others 
after  v.  KUPFFER.) 

BP.  Blastopore.  C.  Coelenteron.  CH.  Notochord.  DL.  Dorsal  lip  of  blastopore.  EC. 
Ectoderm.  EN.  Entoderm.  EP.  Epiphysis.  G.  Gut.  H.  Heart.  M.  Central  nervous 
system.  MES.  Mesoblast.  N.  Nasal  pit.  NC.  Neurenteric  region.  S.  Mouth  pit,  stomo- 
dceum.  SC.  Segmentation  cavity.  T.  Thyroid  gland.  Y.  Yolk  and  yolk  cells. 


DEVELOPMENT   OF  FISHES 

proximately  at  right  angles  to  the  first ;  the  third,  which 
shortly  appears,  is  horizontal  (Fig.  202),  giving  rise  to  the 
stage  of  eight  blastomeres ;  this  plane,  passing  slightly 
above  the  equator,  causes  the  upper  blastomeres  to  be 
slightly  smaller  in  size  than  those  of  the  lower  hemisphere. 
The  amount  of  yolk  in  the  egg,  it  is  accordingly  inferred, 
although  not  sufficient  to  prevent  the  passage  of  cleavage 
planes,  is  enough,  nevertheless,  to  retard  the  nuclear  cleav- 
ages in  the  region  of  the  lower,  or  vegetative,  pole.  In 
Fig.  203,  showing  a  vertical  section  of  the  following 
stage,  another  horizontal  cleavage  has  been  established  in 
the  upper  part  of  the  egg ;  the  segmentation  cavity  is  seen 
in  the  centre  of  the  figure  arising  as  the  central  space 
between  the  blastomeres.  This  is  seen  to  have  become 
greatly  enlarged  in  Fig.  204,  a  slightly  later  stage  where 
in  vertical  section  is  seen  a  greatly  increased  number  of 
blastomeres.  Repeated  cleavage  of  all  blastomeres  now 
continues  regularly,  and  results  in  the  production  of  a 
blastula,  a  smooth-surfaced  cell  mass  containing  the  seg- 
mentation cavity,  SC  (in  section,  Fig.  205) ;  this  is  seen 
to  be  located  in  the  region  of  the  animal  pole.  In  the 
next  developmental  stage,  gastrula,  seen  in  section  in 
Fig.  206,  the  primitive  digestive  tract,  coelenteron,  C,  is 
appearing ;  it  arises  as  an  indentation  of  the  side  of  the 
blastula.  The  ccelenteron,  soon  greatly  increasing  in  depth, 
reduces  in  size  and  finally  obliterates  the  segmentation  cav- 
ity, taking  the  position,  C,  shown  in  section  in  Fig.  207. 
Here  the  segmentation  cavity  has  practically  disappeared ; 
the  surface  opening  of  the  ccelenteron  is  the  blast  op  ore, 
BP\  the  cell  layer  of  the  gastrula's  surface  is  the  ecto- 
derm, EC\  the  cell  layer  lining  the  ccelenteron  is  the  en- 
toderm,  EN:  the  ccelenteron,  it  will  be  seen,  is  closely 
apposed  to  the  ectoderm  at  the  left  of  the  figure,  —  the 


DEVELOPMENT   OF  LAMPREY  lgl 

future  dorsal  region  of  the  embryo ;  on  this  side  the 
margin  of  the  blastopore  is  known  as  the  dorsal  lip,  DL, 
while  to  the  right  the  ventral  lip  is  seen  greatly  enlarged 
by  the  yolk-bearing  cells,  Y.  A  somewhat  later  stage 
(Fig.  208)  shows  the  blastopore  as  a  narrowly  constricted 
opening,  BP,  whose  dorsal  lip  is  slightly  raised  at  its  left- 
hand  margin.  The  head  of  the  embryo  is  to  arise  near 
the  opposite  pole  (as  in  Fig.  210),  and  is  thence  to  elon- 
gate into  neck  and  trunk  (Fig.  212).  A  sagittal  section  of 
a  stage,  slightly  older  than  Fig.  208,  shows  admirably  the 
structures  of  the  embryo  that  have  thus  far  been  differ- 
entiated (Fig.  209).  Contrasting  with  Fig.  207,  it  will 
thus  be  seen  that  the  coelenteron,  arising  at  BP,  has 
become  greatly  elongated ;  at  its  blind  end  its  lining  mem- 
brane, entoderm,  EN,  is  in  contact  with  an  indented  por- 
tion of  the  ectoderm,  at  5,  where  later  the  opening  of  the 
mouth  will  be  established  ;  and  that  ventrally  the  coelen- 
teron has  given  off  a  pouch  which  passes  into  the  yolk,  and 
will  later  be  differentiated  as  the  liver.  That  the  entire 
dorsal  wall  of  the  coelenteron  has  become  thickened,  con- 
stitutes the  main  difference  between  the  sections  of  Figs. 
207  and  209 ;  there  have,  in  other  words,  arisen  between 
the  entoderm  and  ectoderm  of  Fig.  207  the  central  ner- 
vous system,  or  medullary  cord,  M,  and  the  notochord,  CH. 
The  origin  of  these  structures  may  best  be  traced  in  the 
cross-section  of  a  slightly  earlier  stage  (Fig.  213)  ;  the 
coelenteron,  or  gut,  is  at  G,  the  ectoderm  at  EC,  the  yolk 
cells  intervening  at  Y\  and  the  notochord  and  medullary 
cord,  CH,  and  M,  in  the  sagittal  region  immediately  be- 
tween the  gut  and  the  ectoderm.  In  the  medullary  region 
the  ectoderm  cells  are  seen  pressed  together,  growing  down- 
ward and  sidewise,  forming  altogether  a  compact  cell  cord  * 

*  As  in  Teleosts,  but  unlike  other  vertebrates. 


DEVELOPMENT   OF  FISHES 

passing  down  the  back  of  the  embryo  ;  the  notochord  is  aris- 
ing from  the  differentiating  cells  of  the  roof  of  the  gut.  In 
the  cross-section  shown  in  Fig.  214,  the  subsequent  con- 
ditions of  these  structures  may  be  seen ;  the  medullary 
nerve  cord,  M,  is  now  in  section  elliptical,  separated  dor- 
sally  from  the  ectoderm,  and  its  cellular  elements  are  of 
more  uniform  size,  arranged  with  bilateral  symmetry,  its 
central  lumen  having  not  as  yet  appeared ;  the  notochord, 
now  constricted  off  from  the  wall  of  the  gut,  takes  upon 
it  its  characteristic  form  and  structure.  It  is,  however, 
in  the  differentiation  of  the  walls  of  the  gut  that  this 
section  is  of  especial  interest ;  the  gut  is  seen  to  have 
greatly  enlarged,  and  at  the  expense  of  the  yolk  material ; 
its  lining  membrane,  entoderm,  EN,  is  now  directly  ap- 
posed  to  the  outer  germ  layer,  ectoderm,  EC.  The  middle 
germ  layer,  mesoderm,  MES,  —  out  of  which  cartilage, 
muscular  and  connective  tissue,  are  formed, — is  now  seen 
taking  its  origin  as  paired  evaginations  of  the  dorsal  wall 
of  the  gut.  The  mesoderm  shortly  loses  its  connection 
with  the  entoderm,  and  by  the  rapid  increase  of  its  cellular 
elements  rapidly  invests  the  remaining  embryonic  struct- 
ures ;  its  segmental  character  may  be  seen  in  the  surface 
view  shown  in  Fig.  210,  its  dorsal  portions  appearing  as 
the  primitive  segments. 

Later  developmental  stages  are  shown  in  the  sagittal 
sections,  Figs.  211,  212.  These  may  best  be  compared 
with  Fig.  209.  In  Fig.  211  the  head  end  of  the  body  has 
greatly  elongated,  and  with  it  the  gut  cavity  has  dilated ; 
entoderm  is  now  composed  of  very  minute  cells,  whose 
nuclei  are  suggested  by  dots ;  the  yolk  has  become  more 
definitely  restricted  to  the  region  of  the  hinder  gut ;  the 
blastopore  is  still  seen ;  at  its  lips  the  germ  layers  are 
alone  fused. 


DEVELOPMENT   OF  FISHES 


II.      The  Development  of  the  Shark 

On  the  side  of  embryology  a  shark  presents  many  points 
of  striking  contrast  to  the  lamprey ;  yet  it  may  in  many 
regards  be  looked  upon  as  archaic  in  its  developmental 
characters.  Its  contrasting  structures  (together  with  those 
of  lung-fish,  Ganoid,  and  Teleost)  may  best  be  reviewed 
in  the  table,  p.  280. 

The  egg  of  the  shark  is  of  large  size,  richly  provided 
with  yolk  material.  When  removed  from  its  membranes, 
it  is  seen  to  be  of  a  bright  orange  colour ;  its  form  is  elon- 
gated, and  the  weight  of  its  pasty  substance  causes  it  to 
assume  a  flattened  ovoid  (Fig.  216).  At  the  upper  pole  of 
the  egg  is  a  small,  light-coloured  spot,  the  germ  disc,  GD, 
which  figures  prominently  in  the  early  stages  of  develop- 
ment. It  would  represent  the  lamprey's  entire  egg,  if  one 
could  imagine  a  point  of  the  lower  pole  of  the  latter  hugely 
dilated  with  yolk.  It  is  in  the  region  of  this  germ  disc 
alone  that  every  process  of  development  as  far  as  gastrula- 
tion  occurs. 

The  segmentation  of  the  germ  disc  is  shown  in  Figs. 
217-220.  In  the  first  of  these  (Fig.  217)  the  germ  is  seen 
to  be  sharply  marked  off  from  the  surrounding  yolk  by  a 
circular  band  ;  two  cleavages  have  traversed  it  in  the  form 
of  narrow  grooves  separating  the  blastomeres.  In  Fig. 
218  the  fifth  cleavage  has  been  completed;  the  furrows 
dividing  irregularly  the  surface  of  the  germ  disc  fade  away 
at  its  periphery.  Fig.  219  represents  a  vertical  section  of 
the  germ  disc  at  this  stage ;  the  upper,  finely  dotted  layer, 
thinning  away  at  either  side,  is  the  germ  disc  ;  the  coarsely 
granular  material  below  is  the  yolk ;  the  depth  of  the 
cleavage  furrows  is  seen,  and  it  will  be  noted  that  up  to 
this  stage  of  development  there  have  been  no  horizontal 


FIG.  216        GD 


218 


219 


Y        CH 

Figs.  216-230.  —  Development  of  shark,  Scyllium  (mainly).  (All  but  216  after  BAL- 
FOUR.)  216.  Egg  freed  from  case  showing  germ  disc  GD.  217.  Germ  disc  at  second 
cleavage.  218.  Germ  disc  at  fifth  (?)  cleavage.  219.  Vertical  section  of  similar  stage. 
220.  Vertical  section  of  slightly  older  germ  disc.  221.  Blastula.  222.  Early  gastrula. 
223.  Blastoderm  showing  early  growth  of  embryo.  224-226.  Slightly  later  stages  of  growth 
of  embryo.  227.  Stage  showing  early  embryo  and  mode  in  which  the  blastoderm  sur- 
rounds yolk.  228.  Early  embryo  viewed  as  a  transparent  object.  229,  230.  Transverse 
sections  of  early  embryo. 

A.  Anal  invagination.  A  U.  Auditory  vesicle.  BP.  Dorsal  lip  of  blastopore.  C. 
Coelenteron.  CF.  Tail  folds.  CH.  Notochord.  CP.  Cephalic  plate.  EC.  Ectoderm. 
EN.  Entoderm.  G.  Gut.  GD.  Germ  disc.  GS.  Gill  slits.  H.  Heart.  HE.  Head 
eminence.  M,  Central  nervous  system.  M' '.  Yolk  nuclei,  merocytes.  MES.  Mesoblast. 
NC.  Neurenteric  canal.  OP.  Optic  vesicle.  PS,  Primitive  segments.  .S.  Mouth  pit, 
stomodaeum.  SC.  Segmentation  cavity. 

194 


DEVELOPMENT   OF  SHARK 


195 


cleavages.  A  stage  in  which  early  horizontal  cleavages 
are  represented  is  shown  in  Fig.  220.  This  may  well  be 
compared  with  the  last  figure ;  the  germ  disc,  while  not 
increasing  in  diameter,  is  now  seen  to  have  multiplied  its 
blastomeres  by  horizontal  cleavages ;  it  is  converted  into 
a  plug-shaped  mass  of  cells,  sunken  into  the  yolk  material. 
At  M'  are  cell  nuclei,  which  have  found  their  way  into  the 
adjacent  yolk,  and  which  there  acquire  a  developmental 
importance.  They  become  the  so-called  merocytes,  or 
yolk  nuclei. 

The  section  of  the  germ  shown  in  Fig.  221  represents 
a  subsequent  stage  of  development ;  the  blastomeres,  by 
continued  subdivision,  have  become  greatly  reduced  in  size, 
and  are  clearly  to  be  distinguished  from  the  smooth-sur- 
faced, yolk-like  material  lying  beneath.  Merocytes,  M', 
are  apparent  in  the  superficial  layer  of  the  yolk ;  they  are 
supposed  to  serve  a  twofold  function,  —  on  the  one  hand,  to 
elaborate  the  yolk  material  and  fit  it  for  the  embryo's  use ; 
on  the  other,  to  supply  the  cells  which  are  being  con- 
tinually added  to  the  germ's  margin.  In  the  figure  a  large 
cavity  is  shown  to  exist  between  the  yolk  and  the  mass  of 
blastomeres.  This  cavity  has  been  identified  as  the  seg- 
mentation cavity,  SC,  and  the  developmental  stage  as  the 
blastula ;  it  is  as  though  the  lower  hemisphere  of  the 
lamprey's  blastula  (Fig.  205)  had  become  enormously 
enlarged,  and  all  traces  of  the  cells  in  the  floor  of  its 
segmentation  cavity  lost,  except  in  the  layer  of  the 
metamorphosed  cells,  the  merocytes. 

In  the  next  growth  process  the  extent  of  the  germ  area 
becomes  greatly  increased ;  the  thick  blastula  is  now 
thinned  out  into  a  surface  layer  of  regular  cells,  an  en- 
larging disc-like  blastoderm,  which  will  eventually  grow 
around  and  enclose  the  entire  egg.  The  blastoderm  of 


196 


DEVELOPMENT   OF  FISHES 


Fig.  223  is  a  pale-coloured  circular  membrane  of  about  a 
half  inch  in  diameter  lying  on  the  surface  of  the  egg. 
Sectioned  at  an  earlier  stage  (Fig.  222)  the  blastoderm  is 
seen  to  present  the  following  contrast  to  the  blastula  of 
Fig.  221  :  the  floor  of  the  segmentation  cavity  has  flattened, 
and  a  sharp  rim  forms  the  outline  of  the  blastoderm  ;  at 
one  side  this  rim  is  seen  to  protrude  ov7er  the  yolk  mass, 
leaving  a  narrow,  fissure-like  cavity  between.  This  stage 
is  identified  as  the  gastrula ;  the  fissure-like  cavity,  the 
coelenteron ;  its  marginal  blastoderm,  the  dorsal  lip  of  the 
blastopore ;  its  ventral  lip,  the  entire  yolk  mass. 

The  growth  of  the  embryo's  form  takes  its  origin  at  the 
blastopore's  dorsal  lip.  In  Fig.  223  the  rim  of  the  blasto- 
derm is  seen  indented  near  the  point  CF,  and  its  thicken- 
ing at  this  region  becomes  more  and  more  marked  in 
subsequent  stages  ;  on  the  other  hand,  the  anterior  por- 
tion of  the  blastoderm,  growing  continually  on  all  sides, 
becomes  excessively  thin,  flattening  itself  tightly  to  the 
yolk,  and  reducing  the  segmentation  cavity  to  the  small 
area  indicated  at  SC.  The  growth  of  the  embryo  in  the 
mid-region  of  the  blastopore's  dorsal  lip  may  next  be 
followed  in  the  stages,  Figs.  224,  225,  226.  The  inden- 
tation of  the  rim  may  thus  be  seen  to  assume  a  creese- 
like  thickening,  thrusting  forward  its  blunt  end,  the  head 
eminence,  HE,  over  the  blastoderm ;  at  the  points  CF, 
the  tail  eminences,  the  rim  of  the  blastoderm  is  thick, 
protruding,  appearing  to  be  pressing  together  in  the 
median  line,  and  causing  the  body  of  the  embryo  to  be 
actually  pushed  into  form  and  thrust  above  the  level  of 
the  blastoderm.  In  Fig.  225  the  sides  of  the  embryo  are 
separated  dorsally  by  a  deep  groove,  the  medullary  furrow, 
the  future  canal  of  the  central  nervous  system.  In  Fig. 
226  this  is  seen  at  a  more  advanced  stage ;  its  hinder 


DEVELOPMENT   OF  SHARK 


I97 


portion  has  been  roofed  over  by  the  coalesced  sides,  and 
the  process  of  enclosing  the  groove  is  being  continued 
anteriorly,  although  the  head  end  of  the  embryo  is  now 
flattened  out  as  the  prominent  cephalic  plate. 

In  the  stage  figured  in  227,  the  form  of  the  embryo  has 
been  acquired :  the  head  in  the  manner  already  outlined, 
the  tail  by  the  coalescence  and  subsequent  outgrowth 
of  the  tail  folds,  CF.  The  entire  embryo  now  rises  above 
the  blastoderm,  as  this  continues  to  enclose  the  yolk.  In 
the  figure  the  yolk  has  thus  been  more  than  half  enclosed ; 
its  final  appearance  is  seen  in  the  oval  space  outlined  by  a 
dotted  line  behind  the  embryo. 

The  origin  of  the  germ  layers  is  not  as  readily  traced 
as  in  the  Cyclostome.  Ectoderm  is  the  most  clearly 
marked;  even  in  the  blastula  (Fig.  221)  it  has  appeared 
as  an  outer  single-celled  stratum  clearly  differentiated 
from  the  underlying  cells.  Entoderm  is  only  to  be 
seen  on  the  dorsal  wall  of  the  ccelenteron :  the  ventral 
entoderm  (cf.  Fig.  222)  is  merged  with  the  yolk.  Meso- 
derm  takes  its  origin  from  the  inner  layer  on  either  side 
of  the  median  line,  but  it  arises  as  a  solid  cell  mass 
instead  of  as  the  pouch-like  diverticula  in  Petromyzon. 
Cross-sections  of  an  embryo  represented  by  Fig.  224 
have  been  figured  in  Figs.  228  and  229 ;  the  former  is  of 
the  hinder  region  and  illustrates  the  mode  of  growth  of  the 
mesoderm,  MES\  the  latter  across  the  head  region, 
shows  that  in  this  region  the  mesoderm  is  separated 
from  the  inner  layer.  Both  sections  show  the  simple 
character  of  the  medullary  groove,  and  the  latter  section 
the  mode  of  origin  of  the  notochord,  CHt  i.e.  as  an  axial 
thickening  of  the  entoderm. 

An  embryo  of  about  the  stage  of  Fig.  227  is  extremely 
delicate  and  may  readily  be  viewed  as  a  transparent  object. 


198 


DEVELOPMENT   OF  LUNG-FISH 


By  this  time  (Fig.  230)  it  will  be  seen  that  its  prominent 
organs  have  already  been  differentiated.  There  are  thus  : 
medullary  canal,  M,  with  optic,  OP,  and  auditory,  AU, 
vesicles ;  gut  with  gill  slits,  £5,  neurenteric  canal,  NC, 
and  suggestion  of  mouth,  S,  and  anus,  A  ;  notochord, 
CH\  segmented  mesoderm  (primitive  segments),  PS, 
and  heart,  H.  The  medullary  groove  was  converted  into 
a  canal,  as  has  been  already  suggested,  by  the  oyerroofing 
and  fusion  of  the  summits  of  the  medullary  ridges ;  its 
anterior  dilatation  is  the  brain ;  the  gut,  G,  communicates 
freely  below  with  the  yolk  mass ;  it  is  a  cavity,  a  portion 
of  the  coelenteron  that  has  been  constricted  off  with  the 
embryo ;  its  openings,  the  mouth,  anus,  and  gill  slits,  are 
secondary,  acquired  after  there  have  been  established  in 
these  regions  fusions  of  entoderm  and  ectoderm ;  the 
neurenteric  canal,  NC,  a  communication  between  medul- 
lary tube  and  gut,  is  a  structure  acquired  in  the  stage  of 
Fig.  226,  where  the  hinder  medullary  groove  was  roofed 
over,  allowing,  in  the  region  of  the  tail  folds,  a  communi- 
cation to  exist  between  medullary  canal  and  ccelenteron. 
The  notochord  has  by  this  stage  been  completely  sepa- 
rated from  the  entoderm ;  it  already  assumes  a  supporting 
function. 

III.      The  Development  of  Ceratodus 

The  development  of  a  Lung-fish  has  thus  far  been  de- 
scribed (Semon)  only  from  the  outward  appearance  of  the 
embryo.  The  egg  of  Ceratodus  (Fig.  192)  is  seen  without 
its  covering  membranes,  enlarged,  in  Fig.  231.  Its  upper 
pole  is  distinguished  by  its  fine  covering  of  pigment.  The 
first  fine  planes  of  cleavage  are  shown  in  Figs.  232-236 ; 
and  from  these  it  will  be  seen  that  the  yolk  material  of  the 
lower  pole  is  not  sufficient  to  prevent  the  egg's  total  seg- 


234 


239 


244 


245 


246 


Figs.  231-247.  —  Development  of  lung-fish,  Ceratodus.  (After  SEMON.)  X  4-7. 
231.  Egg  immediately  before  cleavage.  232,  233.  First  cleavage,  seen  from  above  and 
from  the  side.  234.  Second  cleavage,  seen  from  above.  235,  236.  Third  cleavage, 
seen  from  above  and  from  the  side.  237.  Blastula.  238,  239.  Gastrulae  showing 
closure  of  blastopore.  240.  Early  embryo,  seen  from  the  side.  241.  Early  embryo 
showing  medullary  folds  (head).  242.  Tail  region  of  same  embryo.  243.  Tail  region 
of  slightly  later  stage.  244.  Head  region  of  same  embryo.  245-247.  Later  embryos. 

A  V.  Auditory  vesicles.  BP.  Blastopore.  GS.  Gill  slits.  M.  Mouth  pit.  MF. 
Medullary  folds'.  O.  Olfactory  lobes.  OP.  Optic  vesicles.  PN.  Primitive  kidney, 
pronephros.  PS.  Primitive  segments.  Y.  Yolk  mass. 

199 


200  DEVELOPMENT   OF  FISHES 

mentation.  The  first  plane  of  cleavage  is  a  vertical  one, 
passing  down  the  side  of  the  egg  (Fig.  233)  as  a  shallow 
surface  furrow,  not  appearing  to  entirely  separate  the  sub- 
stance of  the  blastomeres,  although  traversing  completely 
the  lower  hemisphere  (Fig.  232).  A  second  vertical  furrow 
at  right  angles  to  the  first  is  seen  from  the  upper  pole  in 
Fig.  234 ;  it  is  essentially  similar  to  that  of  Fig.  233.  The 
third  cleavage  of  Fig.  235  is  again  a  vertical  one  (as  in  all 
other  fishes,  but  unlike  Petromyzon),  approximately  meridi- 
onal ;  its  furrows  appear  less  clearly  marked  than  of  earlier 
cleavages,  and  seem  somewhat  irregular  in  occurrence.  The 
fourth  cleavage  is  horizontal  above  the  plane  of  the  equator. 
Judging  from  Semon's  figure  (Fig.  236),  at  this  stage  the 
furrows  of  the  lower  pole  seem  to  have  become  fainter,  if 
not  entirely  lost.  A  blastula  showing  complete  segmenta- 
tion is  seen  in  Fig.  237 ;  the  blastomeres  of  the  upper 
hemisphere  are  the  more  finely  subdivided ;  the  conditions 
of  the  segmentation  cavity  may  be  expected  to  prove 
similar  to  those  of  Fig.  205.  Two  stages  of  the  gastrula 
are  shown  in  Figs.  238  and  239,  showing  a  full  view  of  the 
blastopore.  In  the  earlier  one  (Fig.  238)  the  dorsal  lip  of 
the  blastopore  is  crescent-like ;  in  the  later  (239)  the 
blastopore  acquires  its  oblong  outline,  through  which  the 
yolk  material  is  apparent ;  its  conditions  may  later  be 
compared  to  those  of  a  Ganoid  (Figs.  254,  255). 

The  growth  of  the  embryo  is  illustrated  in  the  remaining 
figures  (Figs.  240-248).  A  side  view  of  an  early  embryo 
is  shown  in  Fig.  240 ;  at  the  top  of  the  egg  to  the  right  is 
the  head  region,  to  the  left  the  blastopore  and  tail.  The 
surface  view  of  the  head  region  (Fig.  241),  the  medullary 
folds,  MF,  may  be  compared  with  those  of  Fig.  225, 
although  they  are  low  and  widely  separated ;  the  axial 
seam  is  referred  to  by  Semon  as  a  demonstration  of  the 


DEVELOPMENT   OF  LUNG-FISH  2QI 

theory  of  the  embryo's  concrescence.  In  the  hinder  region 
of  the  same  embryo  (Fig.  242)  the  blastopore  is  still 
apparent,  BP,  reduced  to  a  narrow,  fissure-like  aperture ; 
around  it  is  the  tail  mass,  corresponding  generally  to  CF 
of  Fig.  226 ;  and  encircling  all  is  the  hinder  continuation 
of  the  medullary  folds. 

The  next  change  of  the  embryo  is  strikingly  amphibian- 
like  ;  the  medullary  folds  rise  above  the  egg's  surface,  and, 
arching  over,  fuse  their  edges  in  the  median  dorsal  line. 
In  Fig.  243,  the  tail  region  of  a  slightly  older  embryo,  this 
process  is  clearly  shown ;  the  medullary  folds,  MFy  are 
seen  closely  apposed  in  the  median  line ;  hindward,  how- 
ever, they  are  still  separate,  and  through  this  opening  the 
blastopore,  BP,  may  yet  be  seen.  At  this  stage  primitive 
segments  are  shown  at  PS\  in  the  brain  region  in  Fig. 
244  the  medullary  folds  are  still  slightly  separated  (cf.  CP, 
Fig.  226). 

Two  views  of  an 
older  embryo  are  fig- 
ured (Figs.  245  and 
246),  where  the  fish- 
like  form  may  be  rec- 
ognized. The  medul-  Fig-  248.— Embryo  of  Ceratodus,  near  the  time 
of  hatching. 

lary  tolas  have  com-      GS.  GUI  slits.   M.  Mouth  pit.    OP.  Optic  vesi- 

pletelv   fused     in    the     deS'    PN'  Primitive  kidney.  pronephros.     T.  Tail 
*  '     eminence. 

median  line,  and  the 

embryo  is  coming  to  acquire  a  ridge-like  prominence; 
optic  vesicles  and  primitive  segments  are  apparent,  and 
at  BP  the  blastopore  appears  to  persist  as  the  anus.  The 
continued  growth  of  the  embryo  above  the  yolk  mass, 
Y,  is  apparent  in  Fig.  247;  the  head  end  has,  however, 
grown  the  more  rapidly,  showing  gill  slits,  GS,  auditory, 
optic,  and  nasal  vesicles,  AU,  OP,  and  O,  at  a  time  when 


202  DEVELOPMENT   OF  GANOID 

the  tail  mass  has  hardly  emerged  from  the  surface.  Pro- 
nephros  has  here  appeared  at  PN  (cf.  with  Fig.  247,  Fig. 
210).  It  is  not  until  the  stage  of  the  late  embryo  of  Fig. 
248  that  the  hinder  trunk  region  and  tail  come  to  '  be 
prominent.  The  embryo's  axis  elongates  and  becomes 
'straighter ;  the  yolk  mass  is  now  much  reduced,  acquiring 
a  more  and  more  oblong  form,  lying  in  front  of  the  tail,  T, 
in  the  region  of  the  posterior  gut  (cf.  Figs.  211  and  212). 
The  head,  and  even  the  region  of  the  pronephros,  PN, 
are  clearly  separate  from  the  yolk  sac ;  the  mouth,  M,  is 
coming  to  be  formed. 

IV.    The  Development  of  Ganoids 

The  development  of  Ganoids  is  next  to  be  outlined. 
The  eggs  of  the  sturgeon  and  gar-pike  are  poorly  provided 
with  yolk.  They  have  still,  however,  a  greater  amount 
than  those  of  the  lamprey  or  lung-fish,  and  in  many 
regards  of  development  suggest  nearnesses  to  the  Elasmo- 
branchs. 

The  egg  of  the  sturgeon  shown  in  Fig.  249  shows 
clearly  two  distinct  zones ;  the  upper,  blotched  with  pig- 
ment at  the  animal  pole,  is  pale  in  colour;  the  lower,  rich 
in  yolk,  is  orange-coloured,  well  speckled  with  pigment. 
The  early  cleavages  appear  at  first  only  in  the  upper  pale- 
coloured  area  which  corresponds  apparently  with  the  germ 
disc  of  the  shark's  egg.  In  Fig.  250  there  have  been 
two  cleavages,  vertical  and  at  right  angles  to  each  other ; 
these  have  sharply  traversed  the  germ  area,  the  earlier 
one  being  now  produced  slightly  into  the  yolk  region  of 
the  egg — only,  however,  as  a  slight  surface  furrow.  The 
third  cleavage  (Fig.  251)  presents  a  stage  closely  corre- 
sponding with  that  of  Ceratodus  of  Fig.  235,  its  plane  tend- 
ing to  pass  parallel  to  the  first  cleavage :  the  germ  disc 


FIG.  249 


250 


251 


252 


258    EC/T  ENNC     259       „ 


Figs.  249-268.  —  Development  of  Ganoids,  Acipenser  and  (last  four  figures)  Lepi- 
dosteus.  x  about  12.  249.  Egg  immediately  before  cleavage.  250.  Second  cleavage. 
251.  Third  cleavage.  252.  Blastula.  253.  Vertical  section  of  blastula.  254.  Early 
gastrula.  255.  Late  gastrula.  256.  Vertical  section  of  late  gastrula.  257.  Early 
embryo.  258.  Sagittal  section  of  same  stage.  259,  260.  Head  and  tail  regions  of 
slightly  later  embryo.  261.  Transverse  body  section  of  hinder  body  region  of  same 
stage.  262,  263.  Head  and  tail  regions  of  late  embryo.  264.  Embryo  immediately 
before  hatching.  265.  Lepidosteus'  blastula.  266.  Vertical  section  of  early  gastrula. 
267.  Late  gastrula.  268.  Embryo,  showing  mode  of  separation  from  yolk. 

BP.  Dorsal  lip  of  blastopore.  C.  Coelenteron.  EC.  Ectoderm.  EN.  Entoderm. 
F.  Pectoral  fin.  GS.  Gill  slits.  H.  Heart.  HE.  Head  eminence.  KV.  Kupffer's 
vesicle.  LC.  Marginal  limit  of  coelenteron.  M.  Mouth  pit.  MC.  Medullary  canal. 
MES.  Mesoblast.  NC.  Neurenteric  canal.  OL.  Olfactory  pits.  OP.  Optic  vesicles. 
PX.  Primitive  kidney,  pronephros.  PS.  Primitive  segments.  SC.  Segmentation 
cavitv.  T.  Tail  eminence.  VL.  Ventral  lip  of  blastopore.  Y.  Yolk,  yolk  mass. 
YP.  'Yolk  plug. 

203 


DEVELOPMENT  OF  FISHES 

is  deeply  cut  by  the  furrows  ;  the  yolk  area,  however,  only 
superficially ;  the  shallow  furrow  of  the  first  cleavage  on 
the  yolk  hemisphere  now  passes  through  the  lower  pole ; 
the  second  cleavage,  passing  downward,  has  made  a  shal- 
low groove  extending  half-way  between  the  rim  of  the 
germ  area  and  the  lower  pole  of  the  egg.  It  is  the  great 
amount  of  yolk  in  the  lower  hemisphere  that  retards  the 
cleavage  of  the  blastomeres.  In  Fig.  252  the  entire 
germ  area  has  become  subdivided  into  a  mass  of  small 
cells,  while  the  large,  irregular  blastomeres  of  the  yolk 
hemisphere  are  separated  only  by  superficial  furrows. 
This  stage,  the  blastula,  is  seen  in  section  in  Fig.  253: 
the  yolk,  unsegmented,  occupies  the  lower  hemisphere ; 
the  germ  area  contains  a  segmentation  cavity,  SC,  with 
a  roofing  of  small  cells,  and  a  floor  of  irregular  cells  half 
engulfed  in  a  deep,  underlying  zone  transitional  between 
germ  and  yolk. 

An  early  gastrula  is  seen  in  Fig.  254 :  the  more  rapid 
multiplication  of  the  cells  of  the  germ  region  has  given 
rise  to  a  down-reaching  cap  of  cells,  whose  boundary  is 
here  sharply  marked  off  from  the  large  and  imperfect  yolk 
cells  of  the  lower  hemisphere.  At  BP,  the  rim  of  the  cell 
cap,  or  blastoderm,  is  sharply  distinct  from  the  yolk ;  it  is 
the  dorsal  lip  of  the  blastopore ;  the  remaining  portion  of 
the  rim  is,  generally  speaking,  the  remainder  of  the  rim 
of  the  blastopore ;  more  accurately  it  is  the  circumcres- 
cence  margin  of  Hertwig.  The  late  gastrula  of  Fig.  255 
shows  the  greatly  increased  extent  of  the  blastoderm  :  its 
margin  is  continually  reducing  the  size  of  the  blastopore, 
BP\  on  its  dorsal  lip  at  HE,  the  outline  of  the  embryo 
is  appearing.  A  sagittal  section  of  this  stage  (Fig.  256) 
shows  at  BP  the  dorsal,  and  at  VL  the  ventral,  lip  of  the 
blastopore  ;  at  YP  the  yolk  material  appears  at  the  egg's 


DEVELOPMENT   OF  GANOID  205 

surface  as  a  plug-like  mass ;  at  SC  is  the  segmentation 
cavity.  The  dorsal  lip  of  the  blastopore  is  seen  to  be  far 
longer  than  the  ventral  lip ;  its  rim  is  the  more  inflected, 
at  KV  occurring  a  recessus  which  the  writer  compares 
to  the  Kupffer's  vesicle  of  Teleost  development;  the 
cavity,  C,  coelenteron,  between  the  wall  of  the  blastopore 
and  the  yolk  mass  is  in  this  region  the  largest.  The 
germ  layers  in  this  stage,  EC,  MES,  EN,  are  seen  to 
be  confluent  at  the  blastopore's  rim ;  at  the  termina- 
tion of  the  coelenteron,  entoderm  and  mesoderm  are 
merged ;  the  ectoderm  forms  the  roof  of  the  segmenta- 
tion cavity. 

The  form  of  the  embryo  next  becomes  more  definitely 
established.  In  Fig.  257  the  blastopore,  much  reduced 
in  size,  is  seen  at  BP ;  its  thickened  rim  is  whitish  in 
colour;  the  darkened  area,  whose  boundary  is  LC,  is  the 
coelenteron,  seen  faintly  through  the  translucent  margin 
of  the  blastopore ;  the  embryo  is  the  opaque  area  of  the 
blastopore's  dorsal  lip,  terminating  anteriorly  in  the  dilated 
tract,  H,  the  head  region.  In  a  sagittal  section  of  a 
slightly  later  stage  (Fig.  258),  the  relations  of  germ 
layers,  EC,  MES,  EN,  coelenteron,  C,  and  yolk  mass, 
Y,  may  be  compared  with  those  of  the  section  (Fig.  256), 
wherein  the  region  YP  corresponds  to  that  of  NC.  A 
thin  ectoderm  will  now  be  seen  to  have  enclosed  the 
entire  egg ;  the  segmentation  cavity  has  disappeared ;  the 
rim  of  the  blastopore,  becoming  continually  constricted, 
causes  the  yolk  material  to  recede  from  the  surface,  and 
leaves  the  blastopore  disappearing,  as  the  blunt  diver- 
ticulum  of  NC.  The  neurenteric  canal,  NC,  is  the  last 
communication  between  the  surface  of  the  egg  and  the 
coelenteron  ;  this  has  become  established  before  the  blas- 
topore closes  in  the  stage  of  Fig.  257  at  its  dorsal  lip; 


206  DEVELOPMENT   OF  FISHES 

the  medullary  furrow  of  the  embryo  has  here  been  the 
deepest,  and  has  been  bridged  over  by  a  coalescence  of 
its  margins.  At  the  anterior  end  of  the  embryo  the 
inner,  EN,  and  middle,  MES,  germ  layers  become 
greatly  thinned,  in  the  region  where  the  heart  is  shortly 
to  arise. 

The  next  stage  of  development  is  represented  in  Figs. 
259,  260,  showing  front  and  hinder  regions  of  the  same 
embryo.  The  curiously  flattened  mode  of  growth  char- 
acteristic of  the  sturgeon  is  here  very  apparent ;  the 
embryo  has  surrounded  over  three-fourths  of  the  egg's 
circumference,  yet  has  not  risen  above  its  surface  curva- 
ture ;  the  head  region  is  especially  flattened ;  mouth,  M, 
heart,  H,  gill  slits,  GS,  brain,  and  optic  vesicles  are  broadly 
spread  out :  the  fourth  ventricle  at  MC,  the  pronephros 
at  PN,  the  primitive  segments  at  PS.  In  the  tail  region 
the  medullary  folds  appear  at  M,  the  pronephric  duct  at 
PN,  the  neurenteric  canal  at  NC.  A  favourable  section 
through  the  hinder  body  region  of  an  early  embryo  is 
shown  in  Fig.  261  ;  it  illustrates  the  mode  of  origin  of  the 
following  structures  :  the  notochord  as  an  axial  thickening 
of  entoderm,  EN,  immediately  under  MC]  the  medullary 
canal,  as  an  infolding  of  (an  under,  or  formative  layer  of) 
the  ectoderm,  its  sides,  folding  over  dorsally,  coming  to  fuse 
in  the  median  line;  the  mesoderm,  MES,  as  in  sharks, 
arising  (partly)  from  the  entoderm  on  either  side  of  the 
notochord. 

The  later  stage,  shown  in  Figs.  262  and  263,  may  be  con- 
trasted with  Figs.  259  and  260;  the  head  region,  though 
still  greatly  flattened  out,  is  now  rising  above  the  surface ; 
the  trunk  region  is  becoming  prominent  ;  the  tail  is  bud- 
ding out,  and  separating  from  the  egg  surface ;  sense 
organs  are  well  outlined,  and  pectoral  fins,  F,  elasmobran- 


DEVELOPMENT  OF  TELEOST  2O/ 

chian  in  character,  are  appearing.  An  embryo  shortly 
before  hatching  is  next  figured  (Fig.  264) ;  the  head  has 
now  entirely  lost  its  flattened  character;  the  mouth  in- 
vagination  occurs  at  M\  the  tail,  much  elongated,  is 
compressed  laterally,  and  already  presents  the  dermal 
embryonic  fin ;  the  yolk  sac  is  attached  along  the  an- 
terior body  region,  in  a  position  more  nearly  that  of  the 
shark  than  of  the  lung-fish. 

Of  the  two  Ganoids,  sturgeon  and  gar-pike,  the  latter, 
as  the  writer  has  pointed*  out,  *  has  the  more  shark-like 
developmental  features.  Its  segmentation  is  incomplete, 
since  the  yolk  pole  of  the  egg  is  at  no  time  traversed  even 
by  superficial  furrows.  The  blastoderm,  or  cell  cap,  is 
early  apparent,  and  is  clearly  marked  off  by  a  furrow  from 
the  irregular  marginal  blastomeres  (Fig.  265).  It  resem- 
bles closely  the  segmented  germ  disc  of  an  Elasmobranch, 
and  the  irregular  marginal  blastomeres  may  be  compared 
to  merocytes.  The  section  of  a  late  blastula  of  Fig.  266 
does  not  differ  widely  from  that  of  the  shark  of  Fig.  221  ; 
a  segmentation  cavity  is  present,  whose  floor  is  smooth, 
and  contains  a  well-marked  zone  of  merocytes,  M\  the 
smaller  quantity  and  firmer  consistency,  perhaps,  of  the 
yolk  do  not,  on  the  other  hand,  permit  the  blastula  to 
occupy  the  sunken  position  of  that  of  the  shark.  In  the 
gastrula  of  the  gar,  further,  a  well-marked  notch  appears 
at  the  dorsal  lip  (as  in  this  stage,  Fig.  223,  of  the  shark), 
representing  the  primitive  blastopore.  And,  finally,  the 
form  of  the  embryo  rises  boldly  from  the  surface,  and 
early  presents  the  well-marked  head  and  tail  eminences, 
HE  and  T,  of  Fig.  268,  comparable  with  Figs.  225  and 
227. 

*  Am.  J.  Morph.,  Vol.  XI,  No.  I. 


FIG.  269 


270 


272 


P     G 


EN 


Figs.  269-283.  —  Development  of  Teleost,  Serranus  atrarius.  (After  H.  V.  WILSON.) 
Fig.  276  X  25.  269.  Egg  immediately  prior  to  segmentation,  showing  position  of  germ 
disc  and  of  oil  globule.  270.  Germ  disc  after  first  cleavage.  271.  Germ  disc  after  third 
cleavage.  272.  Vertical  section  of  blastula.  273.  Vertical  section  of  blastula,  showing 
origin  of  periblast.  274.  View  of  marginal  cells  of  blastula  of  similar  stage.  275.  Growth 
of  blastoderm  around  yolk  mass.  276.  A  slightly  later  stage,  showing  growth  of  embryo. 
277.  Continued  growth  of  embryo  and  reduction  in  size  of  the  blastopore.  278.  Sagittal 
section  of  tail  region  of  embryo  of  last  figure.  279,  280,  281.  Cross-sections  of  embryos, 
showing  successive  stages  in  the  development  of  notochord,  gut,  neuron,  mesoblast.  282. 
Cross-section  of  young  embryo,  showing  the  mode  of  formation  of  gill  slit.  283.  Embryo 
shortly  before  hatching. 

A.  Anus.  AU.  Auditory  vesicle.  BP.  Dorsal  lip  of  blastopore.  Cff.  Notochord. 
EC.  Ectoderm.  EN.  Entoderm.  G.  Gut.  GD.  Germ  disc.  GR.  Germ  ring.  GS. 
Gill  slit.  H.  Heart.  HP.  Head  process.  KV.  Kupffer's  vesicle.  M.  Spinal  nervous 
system.  MES.  Mesoblast.  MP.  Marginal  periblast  cells.  OG.  Oil  globule.  OL.  Ol- 
factory pit.  OP.  Optic  capsule.  P.  Periblast.  PS.  Primitive  segments.  SC.  Segmen- 
tation cavity.  SCH.  Subnotochordal  rod.  TM.  Tail  mass.  Y.  Yolk. 

208 


DEVELOPMENT   OF  TELEOST  2OQ 


V.    The  Development  of  Teleost 

The  mode  of  development  of  bony  fishes  differs  in 
many  and  apparently  important  regards  from  that  of 
their  nearest  kindred,  the  Ganoids.  In  their  eggs  a  large 
amount  of  yolk  is  present,  and  its  relations  to  the  embryo 
have  become  widely  specialized. 

As  a  rule,  the  egg  of  a  Teleost  is  small,  perfectly  spheri- 
cal, and  enclosed  in  delicate  but  greatly  distended  mem- 
branes (Fig.  269).  The  germ  disc,  GD,  is  especially 
small,  appearing  on  the  surface  as  an  almost  transparent 
fleck  ;  it  may  occupy  the  same  position  as  in  the  other 
fishes,  or,  as  in  the  figure,  it  may  occur  at  the  lowermost 
pole.  Among  the  fishes  whose  eggs  float  at  the  surface 
during  development,  as  of  many  pelagic  Teleosts,  e.g.  the 
Sea-bass,  Serranus  atrarius,  —  to  which  all  the  accom- 
panying figures  refer, — the  yolk  is  lighter  in  specific 
gravity  than  the  germ;  it  is  of  fluid-like  consistency, 
almost  transparent.  In  the  yolk  at  the  upper  pole  of 
the  egg  an  oil  globule,  OG,  usually  occurs  ;  this  serves 
to  lighten  the  gravity  of  the  entire  egg,  and  from  its 
position  must  aid  materially  in  keeping  this  pole  of  the 
egg  uppermost. 

The  early  segmentation  of  the  germ  is  seen  in  Figs. 
270,  271.  In  the  former,  the  first  cleavage  plane  is  estab- 
lished, and  the  nuclear  divisions  have  taken  place  for  the 
second  ;  in  the  latter,  the  third  cleavage  has  been  com- 
pleted. As  in  other  fishes  these  cleavages  are  vertical, 
the  third  parallel  to  the  first.  A  segmentation  cavity, 
SCj  occurs  as  a  central  space  between  the  blastomeres, 
as  it  does  in  the  sturgeon  and  gar-pike. 

Stages  of  late  segmentation  are  seen  in  section  in  Figs. 
272,  273.  In  both  the  segmentation  cavity,  SC,  is  greatly 


DEVELOPMENT   OF  FISHES 

flattened,  but  extends  to  the  marginal  cells  of  the  germ 
disc ;  in  Fig.  272  its  roof  consists  of  two  tiers  of  blasto- 
meres,  its  floor  a  thin  film  of  the  unsegmented  substance 
of  the  germ ;  the  marginal  blastomeres  are  continuous 
with  both  roof  and  floor  of  the  cavity,  and  are  produced 
into  a  thin  film  which  passes  downward,  around  the  sides 
of  the  yolk.  In  Fig.  273  the  segmentation  cavity  is  still 
further  flattened ;  its  roof  is  now  a  dome-shaped  mass  of 
blastomeres ;  the  marginal  cells  have  multiplied,  and  their 
nuclei  are  seen  in  the  layer  of  the  germ,  P,  below  the 
plane  of  the  segmentation  cavity.  These  are  seen  at  MP 
in  the  surface  view  of  the  marginal  cells  of  this  stage 
(Fig.  274) ;  they  are  separated  by  cell  walls  only  at  the 
sides ;  below  they  are  continuous  in  the  superficial  down- 
reaching  layer  of  the  germ.  The  marginal  cells,  MP, 
shortly  lose  all  traces  of  having  been  separate;  their 
nuclei,  by  continued  division,  spread  into  the  layer  of  germ 
flooring  the  segmentation  cavity,  and  into  the  delicate  film 
of  germ  which  now  surrounds  the  entire  yolk.  Thus  is 
formed  the  periblast  of  teleostean  development,  which  from 
this  point  onward  is  to  separate  the  embryo  from  the  yolk ; 
it  is  clearly  the  specialized  inner  part  of  the  germ,  which, 
becoming  fluid-like,  loses  its  cell  walls,  although  retaining 
and  multiplying  its  nuclei.  It  would  accordingly  corre- 
spond to  that  portion  of  the  germ  of  the  sturgeon  in  Fig. 
253  which  lies  below  the  plane  of  the  segmentation  cavity, 
and  which  extends  downward  at  the  sides  of  the  yolk ;  in 
this  case,  however,  the  surface  outlines  of  the  cells  have 
not  been  lost.  It  will  be  seen  from  later  figures  (Figs. 
278-282)  that  the  periblast,  P,  comes  into  intimate  rela- 
tions with  the  growing  embryo ;  it  lies  directly  against 
it,  and  appears  to  receive  cell  increments  from  it  at  various 
regions ;  on  the  other  hand,  the  nuclei  of  the  periblast, 


DEVELOPMENT   OF  TELE  OS  T  211 

from  their  intimate  relations  with  the  yolk,  are  supposed 
to  subserve  some  function  in  its  assimilation. 

Aside  from  the  question  of  periblast,  the  growth  of 
the  blastoderm  appears  not  unlike  that  of  the  sturgeon. 
From  the  blastula  stage  of  Fig.  273  to  that  of  the  early 
gastrula  (Fig.  275),  the  changes  have  been  but  slight ;  the 
blastoderm  has  greatly  flattened  out  as  its  margins  grow 
downward,  leaving  the  segmentation  cavity  apparent  at 
SC.  The  rim  of  the  blastoderm  has  become  thickened, 
as  the  'germ  ring;'  and  immediately  in  front  of  BP,  the 
dorsal  lip  of  the  blastopore,  its  thickening,  as  in  Fig.  255, 
marks  the  appearance  of  the  embryo.  In  Fig.  276  the 
germ  ring,  GR,  continues  to  grow  downward,  and  shows 
more  prominently  the  outline  of  the  embryo ;  this  now 
terminates  at  HP,  the  head  region ;  while  on  either  side 
of  this  point  spreads  out  tail-ward  on  either  side  the  indefi- 
nite layer  of  outgrowing  mesoderm,  MES.  In  the  stage 
of  Fig.  277  the  closure  of  the  blastopore,  BP,  is  rapidly 
becoming  completed ;  in  front  of  it  stretches  the  widened 
and  elongated  form  of  the  embryo.  A  sagittal  section 
through  a  late  stage  of  the  blastopore  appears  in  Fig.  278 ; 
with  it  may  be  compared  the  corresponding  region  of  the 
sturgeon  of  Fig.  256;  the  yolk  plug,  YP,  of  the  latter  is 
now  replaced  by  periblast,  P,  the  dorsal  lip  at  BP,  by 
TM,  the  tail  mass,  or  more  accurately  the  dorsal  section 
of  the  germ  rim ;  the  coelenteron  under  the  dorsal  lip 
has  here  disappeared,  on  account  of  the  close  approxima- 
tion of  the  embryo  to  the  periblast  ;  its  last  remnant, 
the  Kupffer's  vesicle,  KV,  is  shortly  to  disappear.  At 
TM,  the  germ  layers  become  confluent  as  at  BP  in  Fig. 
256,  but,  unlike  the  sturgeon,  the  flattening  of  the  dorsal 
germ  ring,  TM,  does  not  permit  the  formation  of  a  neu- 
renteric  canal. 


2J2  DEVELOPMENT  OF  FISHES 

The  process  of  the  development  of  the  germ  layers 
in  Teleosts  appears  an  abbreviated  one,  although  in  many 
of  its  details  it  is  but  imperfectly  known.  In  the  develop- 
ment of  the  medullary  groove,  as  an  example,  the  follow- 
ing peculiarities  exist :  the  medullary  region  at  HP  (Fig. 
276)  is  but  an  insunken  mass  of  cells  without  a  trace  of 
the  groove-like  surface  indentation  of  Fig.  261  or  229. 
Its  condition  is  figured  at  Mm  Fig.  282.  It  is  only  later, 
when  becoming  separate  from  the  ectoderm,  EC,  that  it 
acquires  its  rounded  character  (Fig.  279),  M;  its  cellular 
elements  then  group  themselves  symmetrically  with  refer- 
ence to  a  sagittal  plane,  where  later  by  their  disassocia- 
tion  (?)  the  canal  of  the  spinal  cord  is  formed  (Fig.  280),  M. 
The  growth  of  the  entoderm  is  another  instance  of  special- 
ized development.  In  the  section  of  the  embryo  of  Fig. 
279,  the  entoderm  exists  in  the  axial  region,  its  thickness 
tapering  away  abruptly  on  either  side ;  its  lower  surface 
is  closely  apposed  to  the  periblast;  its  dorsal  thickening 
will  shortly  become  separate  as  the  notochord.  In  a  fol- 
lowing stage  of  development  (Fig.  280),  the  entoderm  is 
seen  to  arch  upward  in  the  median  line  as  a  preliminary 
stage  in  the  formation  of  the  cavity  of  the  gut.  Later, 
by  the  approximation  of  the  entoderm  cells  in  the  median 
ventral  line,  the  condition  of  Fig.  281  is  reached,  where  the 
completed  gut  cavity  exists  at  G. 

The  formation  of  the  mesoderm  in  Teleosts  is  not  defi- 
nitely understood.  It  is  usually  said  to  arise  as  a  process 
of  '  delamination,'  i.e.  detaching  itself  in  a  mass  from  the 
entoderm.  Its  origin  is,  however,  looked  upon  generally 
as  of  a  specialized  and  secondary  character. 

The  mode  of  formation  of  the  gill  slit  of  a  Teleost  does 
not  differ  from  that  in  other  groups  ;  an  evagination  of 
the  entoderm,  GS  (Fig.  282),  coming  in  contact  with  an 


LARVAL  FISHES 

invaginated  tract  of  ectoderm,  EC,  fuses,  and  at  this  point 
an  opening  is  later  established. 

In  Fig.  283  has  been  figured  a  late  embryo.  This  may 
be  compared  with  that  of  the  sturgeon  of  Fig.  264.  The 
Teleost,  though  of  rounded  form,  is  the  more  deeply  im- 
planted in  the  yolk  sac ;  it  is  transparent,  allowing  noto- 
chord,  primitive  segments,  heart,  and  sense  organs  to  be 
readily  distinguished ;  at  about  this  stage  both  anus,  A, 
and  mouth,  M,  are  making  their  appearance. 

D.    THE   LARVAL   DEVELOPMENT   OF  FISHES 

When  the  young  fish  has  freed  itself  from  its  egg  mem- 
branes, it  gives  but  little  suggestion  of  its  adult  form.  It 
enters  upon  a  larval  existence,  which  continues  until  matu- 
rity. The  period  of  metamorphosis  varies  widely  in  the 
different  groups  of  fishes  —  from  a  few  weeks'  to  longer 
than  a  year's  duration  ;  and  the  extent  of  the  changes  that 
the  larva  undergoes  are  often  surprisingly  broad,  invest- 
ing every  organ  and  tissue  of  the  body,  —  the  immature 
fish  passing  through  a  series  of  form  stages  which  differ 
one  from  the  other  in  a  way  strongly  contrasting  with  the 
mode  of  growth  of  amniotes ;  since  the  chick,  reptile,  or 
mammal  emerges  from  its  embryonic  membranes  in  nearly 
its  adult  form. 

The  fish  may,  in  general,  be  said  to  begin  its  existence 
as  a  larva  as  soon  as  it  emerges  from  its  egg  membranes. 
In  some  instances,  however,  it  is  difficult  to  decide  at  what 
point  the  larval  stage  is  actually  initiated  :  thus  in  sharks, 
the  excessive  amount  of  yolk  material  which  has  been  pro- 
vided for  the  growth  of  the  larva  renders  unnecessary  the 
emerging  from  the  egg  at  an  early  stage ;  and  the  larval 
period  is  accordingly  to  be  traced  back  to  stages  that  are 
still  enclosed  in  the  egg  membranes.  In  all  cases  the 


DEVELOPMENT   OF  FISHES 

larval  life  may  be  said  to  begin  when  the  following  con- 
ditions have  been  fulfilled :  the  outward  form  of  the  larva 
must  be  well  defined,  separating  it  from  the  mass  of  yolk,, 
its  motions  must  be  active,  it  must  possess  a  continuous 
vertical  fin  fold  passing  dorsally  from  the  head  region 
to  the  body  terminal,  and  thence  ventrally  as  far  as  the 
yolk  region;  and  the  following  structures,  characteristic 
in  outward  appearance,  must  also  be  established,  the  sense 
organs,  —  eye,  ear  and  nose, — mouth  and  anus,  and  one 
or  more  gill  clefts. 

Among  the  different  groups  of  fishes  the  larval  changes 
are  brought  about  in  widely  different  ways.  These  larval 
peculiarities  appear  at  first  of  far-reaching  significance, 
but  may  ultimately  be  attributed,  the  writer  believes, 
to  changed  environmental  conditions,  wherein  one  proc- 
ess may  be  lengthened,  another  shortened.  So  too  the 
changes  from  one  stage  to  another  may  occur  with  sur- 
prising abruptness.  As  a  rule,  it  may  be  said  the  larval 
stage  is  of  longest  duration  in  (I)  the  Cyclostomes,  and 
thence  diminished  in  length  in  (II)  Sharks,  (III)  Lung- 
fishes,  (IV)  Ganoids,  and  (V)  Teleosts ;  in  the  last-named 
group,  a  very  much  curtailed  (i.e.  precocious)  larval  life 
many  often  occur. 

I.    Larval  Cyclostomes 

The  Cyclostome  larva  is  represented  in  a  stage  as 
early  as  that  of  Fig.  212  :  its  form  is  here  retort-shaped  ; 
the  yolk  material  is  concentrated  in  the  ventral  region 
immediately  in  front  of  the  blastopore  (the  anus  ?),  but 
is  distributed  in  addition  in  the  cells  of  other  body  regions. 
In  the  section  of  a  slightly  older  larva  (Fig.  215),  in  which 
the  mouth  is  all  but  established,  the  form  outline  has 
become  regular,  the  bulk  of  the  yolk,  Y,  restricted  to  the 


LARVAL   SHARKS 


215 


cavity  of  the  intestine,  the  only  instance  of  this  condition 
known  among  fishes  (Ceratodus  ?),  and,  with  but  a  single 
exception  (Ichthyophis),*  among  all  other  vertebrates. 
The  larval  lamprey  is  by  this  time  a  quarter  of  an  inch 
long,  yellowish  white  in  colour ;  its  movements  are  slug- 
gish, rarely  more  than  to  cause  it  to  wriggle  worm-like 
from  the  bottom.  A  few  weeks  later  it  has  acquired  its 
brownish  grey  colour,  its  fin  fold  is  well  marked,  and  its 
habit  is  active ;  it  now  feeds  on  muddy  ooze  rich  in 
organic  matter.  It  'by  this  time  possesses  the  essential 
characters  of  the  well-grown  larva,  long  looked  upon 
as  a  distinct  genus,  Ammoccetes.  In  its  larval  stage  the 
lamprey  appears  to  live  a  number  of  years ;  in  Petromyzon 
planeri  the  adult  stage  is  said  to  be  sometimes  deferred 
until  the  autumn  of  the  fourth  or  fifth  year.  The  trans- 
formation is  then  a  surprisingly  sudden  one ;  the  head 
.attains  its  enlarged  size,  the  mouth  its  ring-like  and  suc- 
torial character,  losing  its  more  anterior  position,  and  its 
lip-like  flaps  (cf.  Fig.  72,  C,  D) ;  teeth  are  developed  in  place 
of  the  numerous  mouth  papillae ;  gills,  formerly  simpler 
in  character,  opening  directly  from  neck  surface  to  gullet, 
now  enter  the  branchial  chamber,  a  ventral  diverticulum 
of  the  gullet ;  eyes  become  prominent,  complete  their 
development,  and  attain  the  head  surface ;  unpaired  fin, 
formerly  of  great  extent,  is  now  reduced  to  its  adult 
position  and  proportions. 

II.    Larval  Sharks 

The  larval  history  of  Sharks  has  been  summarized  in 
Figs.  284-289 :  the  younger  of  these  stages  (Figs.  284, 
285,  286)  have  not  as  yet  escaped  from  their  egg  mem- 
branes. The  hatching,  in  fact,  of  the  young  shark  is 

*  The  writer  has  not  confirmed  Salensky's  observation  upon  the  sturgeon. 


FIG.  284. 


287 


Figs.  284-289.  —  Larval  sharks.  (Figs.  284-287  after  BALFOUR.)  284.  Pristiurus 
(embryo,  X  5)  with  yolk  sac  (X  2).  285,  286.  Larvae  of  Scy Ilium.  X  4.  287.  Ventral 
view  of  head  of  larval  Scy  Ilium,  slightly  younger  than  that  of  last  figure.  X  8.  288.  Larva 
of  Acanthias.  x  4.  289.  Late  larva  of  Acanthias.  X  |. 

G.  Gills.  GS.  Gill  slits.  PP.  Pectoral  fin.  SP.  Spiracle.  Y.  Yolk  sac.  VS.  Stalk 
of  yolk  sac. 

216 


LARVAL   SHARKS  2I/ 

an  exceedingly  slow  one  ;  Pristiurus  emerges  from  the 
egg  in  about  nine  months,  Scyllium  in  about  seven.  And 
in  consequence  of  the  large  amount  of  yolk  stored  in 
the  yolk  sac,  the  young  shark,  as  in  Fig.  289,  has  fully 
acquired  its  adult  outward  characters  by  the  time  the  yolk 
is  exhausted  and  its  sac  absorbed. 

In  Fig.  284  is  figured  a  stage  in  the  development  of 
Pristiurus  which  may  be  regarded  as  either  embryonic 
or  larval ;  the  form  of  the  larva  is  well  established ;  gill 
clefts,  muscle-plates,  mouth,  and  sense  organs  are  present ; 
but,  on  the  other  hand,  unpaired  fin  and  anus  are  lacking. 
There  is  shown  the  abrupt  constriction,  characteristic  of 
Elasmobranchs,  which  separates  the  animal  from  the  yolk 
sac, — a  construction  which  in  later  stages  becomes  narrow 
and  tubular.  The  relatively  larger  size  of  the  yolk  sac 
in  later  stages  is,  of  course,  the  result  of  the  bulkier  elabo- 
ration of  the  yolk  material. 

The  youngest  stage  (Fig.  284)  shows  prominently  the 
great  enlargement  of  the  anterior  end  of  the  embryo,  a 
marked  cephalic  flexure,  large  optic  capsule,  and  irregular 
gill  slits  of  graded  sizes  ;  a  tubular  tail  end,  bulbous  at 
the  terminal,  where  the  neurenteric  canal  occurs ;  as  yet 
the  nasal  pits  are  in  close  proximity  to  the  mouth.  In  the 
next  stage  (Fig.  285),  the  elongated  trunk  has  its  unpaired 
fin,  the  neurenteric  canal  disappearing;  the  beginnings 
of  the  pectoral  fins  are  noticeable ;  gill  clefts  are  of  more 
uniform  size ;  and  the  anal  region  is  indicated.  In  the 
stage  of  Fig.  286,  further  advances  are  seen  in  the  con- 
stricting off  of  the  unpaired  fins,  the  appearance  of  the 
ventral  and  the  continued  growth  of  the  pectoral  fins ; 
in  the  reduced  foremost  gill  slit  (spiracle)  ;  in  the  jaw 
region,  and,  in  fact,  in  the  entire  shaping  of  the  head  ; 
in  the  appearance  of  the  lateral  line.  In  the  ventral  head 


2I3  LARVAL  DEVELOPMENT 

region  (Fig.  287),  is  to  be  noted  the  prominence  of  the 
mouth  cavity,  and  the  enlarged  gill  arches,  showing  by 
this  time  the  outbudding  branchial  filaments.  In  the 
stage  of  Fig.  288,  the  larva  begins  to  appear  shark-like ; 
the  fins  are  longer  and  more  noticeable,  the  anus  has 
appeared,  and  the  branchial  filaments  by  continued  growth 
protrude  at  all  gill  openings.  The  external  gills  thus 
acquired  are  seen  in  a  later  stage  (Fig.  289)  to  have 
disappeared  ;  they  have  aided,  however,  as  Beard,  Turner, 
and  others  have  shown,  in  absorbing  nutriment,  and  must 
be  looked  upon  as  an  especial  organ  of  the  larval  life  of 
the  animal.  Fig.  289  illustrates  a  final  larval  stage :  in  it 
there  appear  all  of  the  structures  of  the  adult  outward  form, 
e.g.  shagreen,  fin  spines,  nictitating  membrane,  anterior 
and  posterior  nasal  openings.  This  larva  has  been  esti- 
mated to  be  about  a  year  older  than  that  of  Fig.  284. 

III.    Larval  Lung-fish 

The  larval  history  of  the  lung-fish,  Ceratodus,  as  recently 
described  by  Semon,  seems  to  offer  characters  of  excep- 
tional interest,  uniting  features  of  Ganoids  with  those  of 
Cyclostomes  and  Amphibians. 

The  newly  hatched  Ceratodus  (Fig.  290)  does  not 
strikingly  resemble  the  early  larva  of  shark  (Fig.  284). 
No  yolk  sac  occurs,  and  the  distribution  of  the  yolk 
material  in  the  ventral  and  especially  the  hinder  ventral 
region  is  suggestive  rather  of  lamprey  or  amphibian ;  it 
is,  in  fact,  as  though  the  quantum  of  yolk  material  had 
been  so  reduced  that  the  body  form  had  not  been  con- 
stricted off  from  it.  The  caudal  tip  in  this  stage  appears, 
however,  to  resemble  that  of  the  shark,  and  as  far  as  can 
be  inferred  from  surface  views  a  neurenteric  canal  persists. 
Like  the  shark  there  then  exists  no  unpaired  fin ;  the 


FJG.  290 


291 


PS  M 


Figs.  290-295.  —  Larval  lung-fishes,  Ceratodus.  (After  SEMON.)  X  6.  290. 
Embryo  at  about  the  time  of  hatching.  291.  Young  larva.  292.  Larva  of  two  weeks. 
293.  Larva  of  four  weeks,  ventral  side.  294.  Larva  of  six  weeks.  295.  Larva  of  ten 
weeks. 

A.  Anus.  A  U.  Auditory  vesicle.  E  G.  External  gills.  GS.  Gill  slits.  H.  Heart. 
M.  Central  nervous  system.  MC.  Mucous  canals.  O.  Opercular  flap.  OL.  Olfac- 
tory organ.  PF.  Pectoral  fin.  PN.  Pronephros.  PS.  Primitive  segments.  S.  Mouth 
pit,  stomodaeum. 

2I9 


22O  DEVELOPMENT  OF  FISHES 

gill  slits,  five  (?),  GS,  are  well  separated,  and  there  is  an 
abrupt  cephalic  flexure.  In  this  stage  pronephros  and 
primitive  segments,  PS,  are  well  marked,  and  are  out- 
wardly similar  to  those  structures  in  Ganoid ;  the  mouth, 
S,  is  on  the  point  of  forming  its  connection  with  the 
digestive  cavity ;  the  anus  is  the  persistent  blastopore ; 
the  heart,  well  established,  takes  a  position,  as  in  Cyclo- 
stomes,  immediately  in  front  of  the  yolk  material. 

In  a  later  stage  the  unpaired  fin  has  become  perfectly 
established,  the  tail  increasing  in  length ;  the  gill  slits 
have  now  been  almost  entirely  concealed  by  a  surrounding 
dermal  outgrowth,  the  embryonic  operculum ;  a  trace  of 
the  pectoral  fin,  PF,  appears ;  the  lateral  line  is  seen  pro- 
ceeding down  the  side  of  the  body ;  near  the  anal  region 
the  intestine*  becomes  narrower  and  the  beginnings  of 
the  spiral  valve  appear.  In  a  larva  of  two  weeks  (Fig.  292), 
a  number  of  developmental  advances  are  noticed  :  the  fish 
has  become  opaque,  the  primitive  segments  are  no  longer 
seen;  the  size  of  the  yolk  mass  is  reduced;  the  anal  fin 
fold  appears;  sensory  canals  are  prominent  in  the  head 
region ;  lateral  line  is  completely  established ;  the  rectum 
becomes  narrowed ;  and  the  cycloidal  body  scales  are  already 
outlined.  Gill  filaments  may  still  be  seen  beyond  the  rim  of 
the  outgrowing  operculum.  In  the  ventral  view  of  a  some- 
what later  larva  (Fig.  293),  the  following  structures  are  to 
be  noted  :  the  pectoral  fins  which  have  now  suddenly  budded 
out,f  reminding  one  in  their  late  appearance  of  the  mode  of 

*  The  yolk  appears  to  be  contained  in  the  digestive  cavity  as  in  Ichthy- 
ophis  and  lamprey. 

f  The  abbreviated  mode  of  development  of  the  fins  is  most  interesting  ; 
from  the  earliest  stage  they  assume  outwardly  the  archipterygial  form  ;  the  re- 
tarded development  of  the  limbs  seems  curiously  amphibian-like  ;  the  pec- 
torals do  not  properly  appear  until  about  the  third  week,  the  ventrals  not  until 
after  the  tenth. 


LARVAL    GANOIDS  221 

origin  of  the  anterior  extremity  of  urodele ;  the  greatly  en- 
larged size  of  the  opercular  flap  ;  external  gills,  still  promi- 
nent ;  the  internal  nares,  OL,  becoming  constricted  off  into 
the  mouth  cavity  by  the  dermal  fold  of  the  anterior  lip  (as 
in  some  sharks) ;  and  finally  (as  in  Protopterus  and  some 
batrachian  larvae)  the  one-sided  position  of  the  anus. 

The  larva  of  six  weeks  (Fig.  294)  suggests  the  outline 
of  the  mature  fish  ;  head  and  sides  show  the  various  open- 
ings of  the  tubules  of  the  insunken  sensory  canals ;  and 
the  '  archipterygium '  of  the  pectoral  fin  is  well  defined. 
The  oldest  larva  figured  (Fig.  295)  is  ten  weeks  old ;  its 
operculum  and  pectoral  fin  show  an  increased  size ;  the 
tubular  mucous  openings,  becoming  finely  subdivided,  are 
no  longer  noticeable ;  and  although  the  basal  supports  of 
the  remaining  fins  are  coming  to  be  established,  there  is 
as  yet  little  more  than  a  trace  of  the  ventrals. 

IV.    Larval   Ganoids 

The  larval  forms  of  a  Ganoid,  Acipenser  (Figs.  296- 
302),  resemble  far  more  closely  those  of  the  shark  than  of 
the  lung-fish.  When  newly  hatched,  the  young  sturgeon 
(Figs.  296,  297)  is  attached  to  the  well-rounded  yolk  sac 
situated  in  the  throat  region,  in  exactly  the  position  one 
would  expect  the  yolk  stalk  to  be  situated  if  the  yolk  mass 
were  larger ;  it  resembles  the  shark  larva  of  Fig.  295  in 
its  unpaired  fin,  in  gill  slits,  in  olfactory,  OL,  optic,  OPy 
and  auditory,  A  U,  organs,  and  in  the  fact  that  it  possesses 
even  at  this  stage  a  trace  of  the  neurenteric  canal ;  on  the 
other  hand,  it  suggests  the  Ceratodus  larva  of  Fig.  291  in 
its  stout  trunk  region,  prominent  muscle  segments,  pro- 
nephros,  PN,  and  anus,  A ;  at  the  foremost  corner  of  the 
yolk  sac  are  mouth  pit  (stomodamm,  S)  and  heart.  A 
larva  of  the  second  day  resembles  in  many  features  the 


298 


300 


301 


Figs.  296-302.  —  Larval  sturgeons.  (All  but  Fig.  302  after  KUPFFER.)  Fig.  299,  X  18 ; 
296-300,  X  10 ;  301,  X8;  302,  X  5.  (Enlargement  approximate.)  296,  297.  Larvae 
shortly  after  hatching.  298.  Larva  two  days  old.  299.  Mouth  region  of  larva  of  third 
day.  300.  Larva  of  fourth  day.  301.  Larva  of  twenty-eight  days.  302.  Sturgeon  ol 
twelve  months. 

A.  Anus.  AU.  Auditory  vesicle.  B.  Barbel.  GS,  Gill  slit.  H.  Heart.  OL.  Ol- 
factory pit.  OP.  Optic  vesicle.  PF.  Pectoral  fin.  PN.  Pronephros.  S.  Mouth  pit. 
SP.  Spiracle. 

222 


LARVAL    TELEOSTS  223 

shark  larva  of  Fig.  286:  dorsal,  caudal,  and  anal  regions  are 
outlined  in  the  unpaired  fin ;  a  pectoral  fin  of  a  fin-fold 
character,  PF,  has  appeared;  the  spiracle,  SP,  is  becom- 
ing established.  The  mouth  region  is  more  clearly  indi- 
cated in  this  stage,  S,  but  may  better  be  seen  in  ventral 
view  in  a  slightly  later  larva ;  here  (Fig.  299)  the  posterior 
lip  is  constricted  off  from  the  yolk  region,  and  the  anterior 
lip  is  budding  off  near  the  median  line  a  pair  of  the  tactile 
barbels ;  the  dermal  fold  (operculum)  enclosing  the  gills 
is  in  a  condition  very  similar  to  that  of  Ceratodus  in 
Fig.  293.  A  larva  of  the  fourth  day  (Fig.  300)  shows 
well-marked  advances  :  the  snout  is  elongated  ;  the  opercle 
is  enclosing  the  gills,  which  are  now  seen  to  protrude  as 
external  branchial ;  the  pectoral  fin  elongates  and  is  tend- 
ing to  protrude  its  fin  axis;  body  segments  and  heart  are 
encroaching  into  the  region  of  the  now  elongate  yolk  sac ; 
the  lateral  line  has  been  formed.  In  a  larva  of  four  weeks 
(Fig.  301),  the  essential  outlines  of  the  sturgeon  may  be 
recognized,  although  the  head  appears  of  strikingly  larger 
proportions  :  barbels,  nares,  mouth,  operculum,  and  spiracle 
are  as  in  the  adult ;  fins,  of  the  mature  outlines,  are  want- 
ing in  all  save  basal  supports  ;  yolk  material  has  long  since 
been  exhausted,  A  very  late  larva  (Fig.  302),  supposed  to 
be  twelve  months  old,  differs  outwardly  from  the  sexually 
mature  form  in  but  its  colouring  and  dermal  plates :  those 
of  the  regular  rows  are  of  great  size,  conspicuous  in  their 
abrupt  spines  and  well-roughened  borders  ;  and  those  of  the 
remaining  trunk  integument  are  remarkably  prominent ;  the 
tail  of  the  larva  shows  clearly  its  palaeoniscoid  character. 

V.    Larval  Teleosts 

The    metamorphoses    of    the    newly    hatched    Teleost 
must    finally  be  reviewed ;    they  are  certainly  the   most 


CH         M 


309 


Figs.  303-309.  —  Larvae  of  Teleost,  Ctenolabrus.  (After  A.  AGASSIZ.)  Fig. 
309  X  about  7,  other  figures  X  about  14.  303.  Larva  shortly  after  hatching.  304, 
305.  Larvae  of  first  few  days.  306,  307.  Larva  of  one  week.  308.  Larva  of  two 
weeks  (?).  309.  Final  larval  stage,  four  (?)  weeks. 

A.  Anus.  A  U.  Auditory  vesicle.  CH.  Notochord.  GR.  Gill  protecting  der- 
mal rays.  H.  Heart.  M.  Central  nervous  system.  OL.  Olfactory  capsule.  OP. 
Optic  vesicle.  PF.  Pectoral  fin.  -S.  Stomodaeum. 

224 


LARVAL    TELEOSTS  22$ 

varied  and  striking  of  all  larval  fishes,  and,  singularly 
enough,  appear  to  be  crowded  into  the  briefest  space  of 
time ;  the  young  fish,  hatched  often  as  early  as  on  the 
fourth  day,  is  then  of  the  most  immature  character;  it 
is  transparent,  delicate,  inactive,  easily  injured ;  within 
a  month,  however,  it  may  have  assumed  almost  every 
detail  of  its  mature  form.  A  form  hatching  three  mille- 
metres  in  length  may  acquire  the  adult  form  before  it 
becomes  much  longer  than  a  centimetre. 

The  larval  life  of  the  common  Sea-bream,  or  Gunner, 
Ctenolabrus  cceruleus,  has  been  admirably  figured  by  A. 
Agassiz.  The  newly  hatched  fish  (Fig.  303)  has  the  yolk 
sac  appended  at  the  throat,  as  a  large,  transparent,  if 
slightly  tinted,  globule ;  save  for  its  great  delicacy  and 
transparency,  it  may  generally  be  compared  to  the  corre- 
sponding larva  of  Acipenser  (Fig.  296).  By  the  third  day 
(Fig.  304),  the  yolk  sac  has  become  greatly  reduced,  the 
trunk  elongated,  the  fin  fold  less  conspicuous ;  primitive 
segments  have  appeared ;  the  pectoral  fin  has  arisen,  but 
is  not  of  the  elasmobranch  form  of  the  similar  stage  (Fig. 
298)  of  sturgeon ;  it  is  long,  thin,  transparent,  and  its 
rapid  growth  indicates  its  metamorphosed  character.  The 
mouth,  S,  is  in  this  stage  on  the  point  of  formation.  In 
a  slightly  older  larva  (Fig.  305),  the  yolk  has  almost  dis- 
appeared ;  its  gill  slits,  GS,  and  mouth  have  now  been 
formed,  and  with  the  latter  the  nasal  apertures.  In  a  fol- 
lowing stage  (Figs.  306,  307),  a  well-marked  opercular  fold 
makes  its  appearance ;  pectoral  fins  acquire  their  com- 
pleted outline  and  the  fin  fold  undergoes  changes  :  ante- 
riorly it  acquires  supporting  actinotrichia,  posteriorly  the 
dermal  supports  of  the  caudal  fin  appear  and  at  their  bases 
the  coalesced  radio-basal s ;  a  ganoidean  heterocercy  is 
here  apparent,  its  distal  tip  the  membranous  opisthure,  O. 


226  LARVAL    TELEOSTS 

The  later  larva  (Fig.  308)  is  characterized  by  the  appear- 
ance of  abundant  pigment  masses  (not  shown  in  the 
figure)  in  all  regions  of  the  trunk;  branchiostegal  rays, 
GR,  and  traces  of  pelvic  fins  are  noted  ;  the  caudal  fin 
has  become  separated  from  the  dorsal  and  anal  elements. 
And  finally,  in  the  stage  of  Fig.  309,  the  fish,  although 
still  of  very  small  size,  has  acquired  almost  perfectly  its 
mature  features ;  the  outward  differences  are  only  those 
of  pigmentation  and  fin  proportions. 


LIST   OF   DERIVATIONS    OF    PROPER    NAMES 


Acanthodes,  d/cavflwS^s,  provided  with  spines. 
Acanthopterygii,  aKavQa,  spine,  7rrepv£,  fin(ned). 
Acipenser,  d/aTnycrios,  classic  name  of  sturgeon. 
Actinopterygii,  d/ms,  stout  ray,  7rrepv£,  fin(ned). 
Alopias,  dAwTre/a'as,  classic  name  of  the  fox  shark. 
Amia,  d/xca,  classic  name  of  tunny(  ?)  . 
Amiurus,  d/xta,  Amia,  ovpd,  tail(ed). 
Ammocoetes,  d/x/xos,  sand,  KOLTTTJ,  (a  bed)  abider. 
Anacanthini,  dvd,  without,  aKav0a,  spine. 
Anguilla,  classic  name  of  eel. 
Arthrodira,  apOpov,  joint,  (?)oYs,  double. 
Aspidorhynchus,  doWs,  shield,  pvyx°s?  snout. 

Bdellostoma,  /JSe'AAa,  leech,  (rro/xa,  mouth. 

Belonorhynchus,  j3e\6vrj,  classic  name  of  gar-fish,  pvyxo?>  snout. 


Calamoichthys,  calamus,  a  reed,  tx^,  fish. 

Callichthys,  KaAAos,  beautiful,  tx^us,  fish. 

Callorhynchus,  KoAAos,  beautiful,  pvyxo?'  snout. 

Carassius,  x«Pa£>  classic  name  of  (sea)fish. 

Caturus,  Kara,  on  the  under  side,  ovpd,  tail. 

Cephalaspis,  /ce^>aA^,  head,  doTris,  shield. 

Ceratodus,  Kepas,  horn,  dSow,  tooth  (ed). 

Cestracion,  KeWpa,  classic  name  of  (pavement-toothed)  sea-fish. 

Cheirodus,  xet'p»  hand,  o8ovs,  tooth  (ed). 

Chimaera,  xfyuupaj  fabulous  monster,  —  lion's  head,  goat's  body,  dragon's 

tail. 

Chlamydoselactrf*xAa/>i-u8os,  frilled,  treAdx^,  shark. 
Chondrostei,  xw8pos,  cartilage,  otrreov,  bone(d). 
Cladoselache,  for  Cladodonto-selache,  /cAdSos,  branch,  oSovs,  tooth  (ed), 

aeAdx^  shark. 
Climatius,  /cAi]ua,  a  gradation  (in  allusion,  perhaps,  to  the  graded  row 

of  fin  spines). 

227 


22g  FISHES,    LIVING  AND  FOSSIL 

Coccosteus,  KO'KKOS,  rough  like  a  berry,  ocrre'ov,  bone. 
Ccelacanthus,  KotAos,  hollow,  aKavOa,  spine  (d). 
Crossopterygii,  /cpocro-os,  fringe  or  tassel,  7rrepv£,  fin. 
Ctenodus,  KTCIS  (KT€VOS),  comb,  oSovs,  tooth(ed). 
Cyclostomata,  KwXos,  circular,  oro/Aa,  mouth. 

Dinichthys,  Savos,  terrible,  i'x0u's,  fish. 
Diplognathus,  SiTrAds,  double  (pointed),  yvaflos,  jaw. 
Diplurus,  SiTrAds,  double,  ovpd,  tail(ed). 
Dipnoi,  Sipvoos,  double  breathing. 
Dipterus,  Sis,  two,  Trrepov,  fin(ned). 


Edestus,  eSeorifc,  a  devourer. 

Elasmobranchii,  eAaoyxos,  strap-like,  ftpayx^  gill(ed). 

Elonichthys,  (?)eA.vo>,  to  twist,  ix^?»  fisn- 

Erythrinus,  ept^pos,  red-coloured. 

Eurynotus,  evpvs,  wide,  VWTOS,  back(ed). 

Eusthenopteron,  ew^ev^s,  strong,  TrrepoV,  fin. 

Fierasfer,  derivation  of  Cuvier  uncertain,  perhaps  from  proper  name. 

Gadus,  classic  name  of  cod. 
Ganoid,  yavos,  enamelled. 
Gnathostome,  yvdOos,  jaw,  o-ro/xa,  mouth. 

Gyroptychius,  yOpos,  a  circle,  7rrux«>?»  folded  (referring  to  the  tooth 
enamel). 

Harriotta,  from  the  proper  name  Harriott. 

Hemitripterus,  hemi,  half,  rpeis,  three,  Trrepw,  fin(ned). 

Heptanchus,   eTrra,    seven,   ayx^    (referring    to    the    compressed   gill 

openings). 

Hippocampus,  classic  name,  "  sea-horse." 
Holocephali,  oAos,  whole  or  complete,  Ke<£aA^,  head. 
Holoptychius,  oAos,  entire(ly),  TTTV^OS,  folded  (referring  to  the  tooth 

enamel). 

Hybodus,  v/?os,  hump,  oSous,  tooth. 
Hyperoartia,  vTrepwa,  palate,  aprtos,  entire. 
Hyperotretia,  vTrepwa,  palate,  rperos,  pierced. 


Ichthyotomi,    t'x^us,  fish,  re/xvco,  separate   (referring   perhaps    to   the 

distinctness  of  this  group)  . 
Ischyodus,  I<TXU'S,  power(ful),  oSovs,  tooth(ed). 


DERIVATION  OF  NAMES  22Q 

Laemargus,  classic  name  of  a  shark. 

Lagocephalus,  Xeryws,  rabbit,  /ce^aX*/,  head. 

Lamna,  Xaftvo,  classic  name  for  a  shark. 

Lepidosiren,  XtTri's,  scale  (d),  siren,  salamander. 

Lepidosteus,  X«ris,  scale,  oore'ov,  bone. 

Leptolepis,  XCTTTOS,  smooth  or  delicate,  A.OUS,  scale (d). 

Lophobranchii,  Xo<£os,  tuft,  J3pa.y\iov,  gill(ed). 

Marsipobranchii,  fjapa-Linov,  pouch,  ftpa.y\iai,  gills. 

Megalurus,  /Aeya??  large>  oupo,  tail(ed). 

Microdon,  fUKpos,  small,  oSovs,  tooth  (ed). 

Mormyrus,  classic  name  of  a  (sea)  fish  ( —  from  //.op/xvpo),  I  murmur). 

Myliobatis,  /xvXwxs,  pavement  (toothed),  /3art5,  skate. 

Myiostoma,  /xvXos,  mill(like),  OTO/UUX,  mouth. 

Myriacanthus,  /xvpwis,  ten  thousand,  axav^a,  spine. 

Myxine,  /xv^tvos,  slimy-fish. 

Onychodus,  ow^,  claw;  oSovs,  tooth  (ed). 
Ophidium,  o<^>t'8tov,  a  snake. 
Osteolepis,  ooWov,  bone,  ACTTI'?,  scale  (d). 
Ostracoderm,  oo-rpaKiov,  shell,  8e'p/xa,  skin. 

Palaeaspis,  TroXatos,  ancient,  a(T7ri?,  shield. 

Palaeoniscus,  TroAatos,  ancient,  OI/IO-KOS,  a  sea-fish. 

Palaeospondylus,  TroAato?,  ancient,  <77roV8vAos,  vertebrae. 

Parexus,  ?  Trape^w,  have  as  one's  own  (referring  to  the  peculiar  nature 

of  the  fish?). 

Perca,  classic  name  offish. 
Petromyzon,  TreVpos,  stone,  /xv£ao>,  to  suck. 

Phaneropleuron,  <^>avepos,  well  marked,  TrAevpo,  side  (fins)  or  ribs(?). 
Pisces,  fishes. 

Plagiostomi,  TrAayios,  transverse,  OTO/AO,  mouth. 
Plectognathi,  TrXexTo?,  twisted,  yvdOos,  jaw. 
Pleuracanthus,  TrXevpa,  side,  a/cav^a,  spine. 
Pleuropterygii,  TrXevpa,  side,  Trrepv^,  fin(ned). 
Pogonias,  Trwywvta?,  bearded. 
Polyodon,  TroXvs,  many,  oSwv,  tooth(ed). 
Polypterus,  TroXvs,  many,  Trrepov,  fin(ned). 
Prionotus,  TrptW,  saw,  vturos,  back. 
Pristiophorus,  vpurns,  a  saw,  ^>op£tu,  to  carry. 
Pristis,  TrpiVrts,  a  saw-fish. 
Protopterus,  Trpoiros,  ancient,  Trrepov,  fin(ned). 


230  FISHES,   LIVING  AND  FOSSIL 

Psammodus,  ^a/A/xos,  sand,  o8ovs,  tooth  (ed). 
Psephurus,  t/o^os,  a  little  stone,  ovpa,  tail. 

Pseudopleuronectes,  i/^vSos,  false,  TrAevpw,  side,  vrJKrrjs,  swimmer. 
Pterichthys,  Trrepv^,  fin  or  wing,  ix^^>  ^s^' 


Raja,  classic  name  of  skate. 

Rhabdolepis,  pa/3Sos,  nail,  AcVis,  scale  (d). 

Rhina,  ptvrj,  a  rasp. 

Rhinobatus,  ptVa,  Rhina,  /fori's,  skate. 

Rhynchodus,  pvyx0<*i  snout,  oSov's,  tooth  (ed). 


Scaphirhynchus,  <7Ka<£iW,  shovel, 
Scomberomorus,  (r/co/x^pos,  mackerel,  /u,opiov,  part. 
Scyllium,  crKvAtoi/,  classic  name  of  this  shark. 
Selachii,  o-eAa^ry,  shark. 
Semionotus,  o-^etoj/,  a  standard,  VWTO?,  back. 
Silurus,  classic  name  of  fish. 
Siphostoma,  (n'^on/,  tube,  o-ro/xa,  mouth. 
Sirenoidei,  siren,  salamander,  oTSos,  like. 
Squaloraja,  squalus,  shark,  r<27«,  skate. 
Squalus,  classic  name  of  a  shark. 
Squatina,  a  classic  name  of  a  sea-fish. 

Teleocephali,  reAeos,  entirely,  oo-re'oi/,  bone,  Ke<£aA?j,  head. 

Teleost,  reAeos,  entirely,  oareov,  bone. 

Teleostomi,  re'Aeos,  entirely,  oo-reW,  bone,  oro/m,  mouth. 

Titanichthys,  ///«//,  giant,  IxOvs,  fish. 

Torpedo,  classic  name  (from  the  root  of  Torpor,  stupefy)  . 

Trachosteus,  rpa^'s,  rough,  ocrre'oi/,  bone. 

Trygon,  rpvywv,  the  thorny  ray. 

Urogymnus,  ovpd,  tail,  yv/xvos,  naked. 
Xenacanthus,  £eVos,  strange,  aKavOa,  spine. 


BIBLIOGRAPHY 


IN  the  following  list  the  writer  aims  to  present  the  more  recent  and 
more  important  works  relating  to  the  general  subject  of  fishes.  Titles 
have  been  classified,  and  most  of  the  references  give  more  or  less  com- 
plete bibliographies  of  their  special  subjects.  Of  the  journals  in  which 
papers  occur  the  principal  abbreviations  are  as  follows  :  — 


Q.J.M.S  Quarterly  Journal  of 
Microscopical  Science. 

P  .  Proceedings. 

R.     .     .  Report. 

S .     .     .  Society. 

SB     .     .  Sitzungsberichte. 

Sci     .     .  Science,  or  Scientific. 

Tr.    .     .  Transactions. 

U.S.F.C  United  States  Fishery 
Commission. 

VH    .     .  Verhandlungen. 

Z  .          .  Zeitschrift. 


A    ...  Archiv  (or  Archives) . 

AH      .     .  Abhandlungen. 

Ann.  N.H  Annals  and  Magazine 
of  Natural  History. 

B     .     .     .  Bulletin. 

C.R     .     .  Contes  rendus. 

DS.     .     .  Denkschriften. 

J  Journal 

JB  .     .     .  Jahrbuch 

JH  .     .     .  Jahreshefte 

J.R.M.S  .  Journal  of  the  Royal  Mi- 
croscopical Society. 

MT      .     .  Mittheilungen 

The  Roman  numerals  denote  the  number  of  the  volume,  the  Arabic 
numerals  the  pages. 

WORKS   ON   THE   GENERAL   SUBJECT,   FISHES 

WOODWARD,  A.  SMITH     Catalogue   of  Fossil   Fishes   in  the   British 
Museum.     Vols.  I,  II  (and  III). 

London,  i889~(95). 

GUXTHER,  A.      ...     Catalogue    of    the    Fishes     in    the    British 

Museum.   Vols.  I-VIII.   London,  1859-70. 

GUXTHER,  A.      ...     An  Introduction  to  the  Study  of  Fishes.    8vo. 

pp.  720.    Illustrated.     Edinburgh,  1880. 

GUXTHER,  A.       ...     Fishes :    Challenger  Reports.      Vol.    I,    pt. 
VI,  Vol.  XXXI,  pt.  LXXVIII. 

London,  1880-89. 

GILL,  T Fishes  :  Standard  Natural  History. 

Boston,  1885. 
231 


232  FISHES,   LIVING  AND  FOSSIL 

GOODE,  G.  BROWN  .     .     Fishery  Industries  of  U.  S.     U.  S.  F.  C. 

Washington,  1884. 

DUMERIL,  A Histoire     naturelle     des     Poissons.       Vols. 

I-II    (Sharks,    Chimaeroids,    Lung-fishes, 
Ganoids,  Lophobranchs).          Paris,  1890. 

AGASSIZ,  L Recherches  sur  les  Poissons  Fossiles.     Vols. 

I-V,  with  Atlas  volumes. 

Neuchatel,  1833-43. 
ZITTEL,  K.  v.      ...     Handbuch  der  Palaeontologie.     Fische. 

Munich,  1887. 
ROLLESTON,  G.  .     .     .     Forms  of  Animal  Life.     Second  edition. 

Oxford,  1888. 

HUXLEY,  T Manual    of   the    Comparative    Anatomy    of 

Vertebrated  Animals.        New  York,  1872. 

JORDAN  and  GUILBERT     Manual  of  the  Vertebrates  of  Eastern  N.  A. 
McClurg.     Last  edition. 


SKELETON.  — '86  BAUR,  G.,  Squamosum,  Anat.  Anz.  '87  Ribs, 
Am.  Nat.  xxi,  942-945.  '86  COPE,  E.  D.,  Caudal  vertebrae,  Am. 
Phil.  Soc.  243.  '93  BOULENGER,  G.  A.,  Haemapophyses,  Ann. 
N.H.  xii,  60-61.  '92  DOLLO,  L.,  Ribs,  vertebrae,  B.  Sci.  Fr.  Belg. 
xxiv.  '87  GEGENBAUR,  Occipital  region,  Kolliker  Festschr.  1-33. 
'79  GOETTE,  A.,  Wirbelsaule,  A.  mikr.  Anat.  xvi,  428.  '89  HAT- 
SCHEK,  Rippen,  VH.  Anat.  Gesell.  Berl.  (Jena).  '78  IHERING, 
H.,  Wirbelverdoppelung,  Zool.  Anz.  I,  72-74.  '93  JORDAN,  D.  S., 
Temperature  and  vertebras,  Wilder  Quarter  Century  Book,  Ithaca, 
!3-37-  '93  KLAATSCH,  H.  (Vertebrae),  Morph.  JB.  xix,  649- 
680,  and  xx,  143-186.  '68  KLEIN,  Schadel,  Wiirt.  Nat.  JH.  71- 
171,  and  ('81)  xxxvii,  326-360.  '87  LUOFF,  B.  (Chorda  and 
Sheath),  B.  S.  Mosc.  227-342  (442-482,  German).  '77  PARKER 
and  BETTANY,  Morph.  of  the  Skull,  London,  pp.  14-90.  '89 
POUCHET  and  BEAUREGARD,  Traite  de  Osteol.  Comp.  Paris, 
398-451.  '87  STRECKER,  C.  (Condyles),  A.  Anat.  Phys.  Anat. 
Abth.  301-338. 

INTEGUMENT,  TEETH.  — '92  AGASSIZ,  A.,  Chromatophores,  B. 
Mus.  Comp.  Zool.  xxiii,  189-193.  '82  BAUME,  A.,  Odont.  Forsch. 
Leip.  41-52.  '77  HERTWIG,  O.,  Hautskelet,  Morph.  JB.  II, 
328-395,  and  v  ('79),  1-21.  '90  KLAATSCH,  H.,  Schuppen,  op. 
cit.,  97-202  and  209-258.  '45  OWEN,  Odontography,  London. 
'93  RYDER,  J.  A.,  Mechanical  genesis  of  Scales,  Ann.  N.  H.,  xi, 
243-248.  '82  TOMES,  C.,  Dental  Anat.  Ed.  2. 


BIBLIOGRAPHY:   FISHES 


233 


FINS.  —  '90  COPE,  Homologies,  Am.  Nat.  401-423.  '79  DAVIDOFF, 
M.,  Pelvics,  Morph.  JB.  v,  450-520,  vi  ('80),  125-128,  433-468. 
'87  EMERY,  C,  Homologies,  Zool.  Anz.  x,  185-189.  '65  GEGEX- 
BAUR,  C.,  Brust  Flosse,  Leip.  4to,  pp.  176.  '7O  Jen.  Z.,  v,  and 
('73)  Archipterygium,  vii.  '79  Morph.  JB.,  v,  521-525. 
'94  Op.  cit.  xxi,  119-160.  '89  HATSCHEK  (Paired),  VH.  Anat. 
Gesell.  Berl.  82-90.  '68  PARKER,  W.  K.,  Shoulder  girdlej  Ray 
Society,  Lond.  pp.  237.  '83  RAUTENFELD,  E.  V.,  Ventrals,  Dor- 
pat  ('82),  48  pp.  '79  RYDER,  J.  A.,  Bilateral  symmetry,  Am.  Nat. 
xiii,  41-43.  '85  Unpaired  fins,  op.  cit.  xix,  90-97.  '86  Em- 
bryol.  of  fins,  R.  U.  S.  F.  C.,  981-1086.  '86  Fin  rays  and  degen- 
eration, P.  U.  S.  Nat.  Mus.  71-82.  '87  Homologies,  P.  Acad. 
Philadel.  344-368.  '77  THACHER,  J.,  Homologies,  Tr.  Conn. 
Acad.  III.  '92  WIEDERSHEIM,  R.,  Gliedmassenskelet,  Jena,  266 
pp.  '92  WOODWARD,  A.  S.,  Evolution,  Nat.  Sci.  28-35. 

VISCERA,  GLANDS,  CIRCULATORY.  — '84  AYERS,  H.,  Pori 
abdominales,  Morph.  JB.  x,  344-349.  '89  Carotids,  B.  Mus. 
Comp.  Zool.  xvii.  '82  BALFOUR,  F.  M.,  Head  kidney,  Q.  J.  M.  S. 
xxx,  12-16.  '87  BOAS,  J.  E.  V.,  Arterienbogen,  Morph.  JB.  xiii, 
115-118.  '79  BRIDGE,  T.,  Pori  abdominales,  J.  Anat.  Phys.  xiv, 
81-102.  '85  CLELAND,  J.,  Spiracle,  R.  Br.  Ass.  1069.  '87 
EBERTH,  C.  J.,  Blutplattchen,  Kb'lliker  Festschrift,  37-48.  '66 
GEGENBAUR,  Bulbus,  Jen.  Z.  ii,  365-375.  '84  Abdominal  poren, 
Morph.  JB.  x,  462-464.  '91  Conus,  op.  cit.  xvii,  596,  610.  '85 
GROSGLIK,  S.,  Kopfniere,  Zool.  Anz.  viii,  605-611.  '90  HOWES, 
G.  B.,  Intestinal  canal  and  blood  supply,  J.  Linn.  S.  xxiii,  381-410. 
'64  HYRTL,  J.  (Hepatic  and  portal),  SB.  Acad.  Wiss.  Wien, 
167-175.  '85  PHISALIX,  C.,  Rate,  Paris,  8vo.  '90  ROSE,  C., 
Herz,  Morph.  JB.  xvi,  27-96.  '82  SOLGER,  B.,  Niere,  A.  H.  Gesell. 
Halle,  xv,  405-444.  '84  WELDOX,  W.  F.  R.,  Suprarenals,  P. 
Roy.  S.  xxxvii,  422-425. 

SWIM-BLADDER.  —  '86  ALBRECHT,  P.,  Non-homologie  des 
poumons,  Paris  and  Brux,  44  pp.  '8O  DAY,  F.,  Zool.  97-104. 
'66  GOURIET,  E.,  Ann.  Sci.  Nat.  vi,  369-382.  '73  HASSE,  C., 
Anat.  Studien,  I,  Heft  4.  '90  LIEBREICH,  O.,  A.  Anat.  Phys. 
Phys.  Suppt.  142-161,  360-363.  '85  MORRIS,  C.,  P.  Acad.  Nat. 
Sci.  Philadel.  124-135,  Anat.  Anz.  ('85)  xxvi,  975-986. 

NERVOUS  SYSTEM  AND  END  ORGANS.  — '83  BAUDELOT,  E., 
fol.  Paris,  178  pp.  '88  BATESOX,  Sense  organs,  J.  Mar.  Biol. 
Ass.  I,  No.  2.  '85  BEARD,  J.,  Branchial  sense  organs,  Q.  J.  M.  S. 
xxvi.  '82  BERGER,  E.  (Eye),  Morph.  JB.  viii,  97-168.  '84 
BLAUE,  J.  (Nasal  membrane),  A.  Anat.  Phys.  331-362.  '83 


234 


FISHES,   LIVING  AND  FOSSIL 


CANESTRINI,  Otoliths,  Atti.  Soc.  Pad.  viii,  280-339.  '86  Hearing 
organ,  op.  cit.  ix,  256-282.  '91  CHEVREL,  R.,  Sympathetic, 
These  faculte  des  sciences,  Paris.  '79  DERCUM.  F.,  Lateral  line, 
P.  Acad.  Phil.  152-154.  '70  FEE,  F.,  Systeme  lateral,  Mem.  S. 
Sci.  Nat.  Strasb.  vi,  129-201.  '73  HASSE,  C.,  Gehororgan,  Anat. 
Stud.  I,  Heft  3.  '88  JULIN,  C.,  Epiphysis,  B.  Sci.  Nord.  x,  55-65. 
'90  ?  KOKEN,  E.,  Otoliths,  Z.  geol.  Gesell.  xliii,  154.  '91 
OWSJANNIKOW,  P.  (Pineal  eye),  Rev.  S.  Nat.  St.  Petersb. 
loo-ui.  '81  RETZIUS,  G.,  Gehororgan,  Stockholm,  fol.  222  pp. 
'71  SCHULTZE,  F.  E.,  Seitenlinie,  A.  mikr.  Anat.  vi,  62.  '70 
STIEDA,  L.,  Centralnervensystem,  Z.  wiss.  Zool.  xxi,  273-456. 
EMBRYOLOGY.  — '85  HAACKE,  W.,  Uterinaler  Brutpflege,  Zool. 
Anz.  viii,  488-490.  HALBERTSMA,  H.  J.,  Normal  en  abnormal 
Hermaphroditismus,  Tijd.  Nied.  Dier.  Ver.  Amst.  '87  HOCH- 
STETTER,  F.,  Venensystem,  Morph.  JB.  xiii,  119-172.  '86  HOFF- 
MAN, C.  K.,  Urogenital,  Z.  wiss.  Zool.  xliv,  570-643.  '91  KUPFFER, 
C.  v.,  Kopfniere,  VH.  Anat.  Gesell.  22-55.  '90  LAGUESSE,  E., 
Rate,  J.  de  1'Anat.  Phys.  xxvi,  345-406  and  425-495.  '77 
LANKESTER,  E.  RAY.  Germ  layers,  Q.  J.  M.  S.  xvii.  '93  LWOFF,  B., 
Keimblatterbildung,  Biol.  Centralb.  xiii,  40-50,  76-81.  '79  MAR- 
TENS, E.  V.,  Hermaphroditische  Fische,  Naturf.  116.  '80  Nuss> 
BAUM,  M.,  DhTerenzirung  d.  Geschlechts,  A.  mikr.  Anat.  xviii, 
1-121.  '89  SCHWARZ,  D.,  Schwanzende,  Z.  wiss.  Zool.  xlix, 
191-223.  '92  VIRCHOW,  H.,  Dotterorgan,  Z.  wiss.  Zool.  liii, 
Suppl.  161-206. 

THE   CYCLOSTOMES 

GENERAL.  — '93  AYERS,  H.,  Bdellostoma,  Woods  Holl  Lectures, 
125-161.  '92  BEARD,  J.,  Lampreys  and  Hags,  Anat.  Anz.  viii, 
59-60.  '91  BUJOR,  P.,  La  metamorphose  de  rAmmocoetes,  Rev. 
Biol.  du  Nord  de  la  France,  iii,  pp.  97.  '93  GAGE,  Lake  and 
Brook  Lampreys,  Wilder  Quarter  Century  Book,  Ithaca,  421-493. 
'91  HOWES,  G.  B.,  Lamprey's  affinities  and  relationships,  P. 
Tr.  Liverpool  Biol.  Soc.  vi,  122-147.  '89  JULIN,  C.,  Morphologic 
de  PAmmocrete,  B.  Sci.  France  et  Beige,  281-282.  '90  KAENSCHE, 
C.  C.,  Metamorphose  des  Ammoccetes,  Schneider's  Zool.  Beitrage, 
II,  219-250. 

ANATOMY,  GENERAL.  — '86  CUNNINGHAM,  J.  T.,  Critique  of 
Dohrn's  views  of  Cyclostome  morphology,  Q.  J.  M.  S.  xxvii,  265- 
284.  '88  JULIN,  C.,  Anatomic  de  rAmmocoetes,  B.  Sci.  du  Nord 
de  la  France,  x,  265-295.  '75  LANGERHANS,  P.,  Untersuchungen 
u.  Petromyzon,  VH.  d.  n.  Gesell.  Friburg,  XI,  Heft  3.  '37 


BIBLIOGRAPHY:    CYCLOSTOMES  235 

MULLER,  J.,  Vergleich.  Anat.  d.  Myxinoiden,  AH.  K.  Akad.  Wiss. 
Berlin,  65-340,  9  pis.  '79  SCHNEIDER,  A.,  Beitrage  zur  vergleich. 
Anat.  4to,  pp.  164,  Berlin. 

SKELETON.  — '92  BURNE,  R.,  Branchial  Basket  in  Myxine,  P.  ZooL 
S.  706-708.  '69  GEGENBAUR,  C.,  Sketelgewebe,  Jen.  Z.  V.  '93 
HASSE,  C,  Wirbel.  Z.  wiss.  Zool.  290-305.  '76  HUXLEY,  T. 
H.,  Craniofacial  Apparatus,  J.  Anat.  Phys.  x,  412-429.  ('84) 
PARKER,  W.  K.,  Monograph  of  Skeleton  of  Petrom.  and 
Myxine,  P.  Roy.  S.,  '82,  439-443  and  Phil.  Tr.  Roy.  S.,  '83,  373- 
457.  '78  PEREPELKINE,  K.,  Structure  de  la  Notochorde,  B.  Mosc. 
liii,  107-108.  '92  RETZIUS,  G.,  Caudalskelet  der  Myxine,  BioL 
Foren.  iii,  81-84. 

MUSCULATURE.  — '75  FURBRINGER,  P.,  Muskulatur  des  Kopf- 
skelets,  Jen.  Z.  ix,  N.  F.  II.  '67  GRENACHER,  H.,  Muskulatur,  Z. 
wiss.  Zool.  xvii.  '59  KEFERSTEIN  (Histological),  Du  Bois  R's.  A. 
f.  Anat.  548.  '82  SCHNEIDER,  A.,  u.  d.  Rectus,  Zool.  Anz.  N.  107, 
p.  164.  '52  STANNIUS,  H.  (Heart  fibres),  Z.  wiss.  Zool.  iv,  252. 
'52  (Histology),  L'Institut,  xx,  132-134,  and  Gb'ttin.  Nachricht. 
'51, 225-235.  '82  STEINDACHNER,  A.,  u.  d.  Rectus.  Zool.  Anz.  v, 
660. 

FINS.  — '85  CLELAND,  J.,  Tail  of  Myxine,  R.  Br.  Ass.  Adv.  Sci.  1069. 

INTEGUMENT,  TEETH.  — '88  BEARD,  J.,  Teeth  of  Myxinoids, 
Nature,  xxxvii,  499,  and  Anat.  Anz.  iii,  169-172.  '91  BEHRENS, 
Hornzahne  v.  Myxine,  Zool.  Anz.  xiv,  83-87.  '82  BLOMFIELD, 
S.  E.,  Thread,  cells  of  Epidermis  of  Myx.  Q.  J.  M.  S.  xxii,  355-361. 
'76  FOETTINGER,  A.,  Structure  de  1'Epiderme,  B.  Acad.  roy.  d. 
Beige,  ix,  No.  3.  '94  JACOBY,  M.,  Hornzahne,  A.  mikr.  Anat. 
117-148.  '60  KOLLIKER,  Inhalt  d.  Schleimsacke  d.  Epidermis, 
Wiirzb.  naturwiss.  Zeitschr.  i,  i-io.  '64  MULLER,  H.,  Epidermis, 
Wiirzb.  naturwiss.  Zeitschr.  v,  43-53.  '89  POGOJEFF,  L.,  Haut, 
A.  mikr.  Anat.  xxxiv,  106-122.  '61  SCHULTZE,  M.,  Kolben- 
formig  Gebilde,  A.  Anat.  u.  Phys. 

VISCERA,  GLANDS,  CIRCULATORY.  — '46  DUVERNOY,  G.  L., 
Sinus  veineux  genital,  C.  R.  xxii,  662.  '76  EWART,  T.  C.,  Abdom. 
pores,  J.  Anat.  and  Phys.  x.  '78  Vascular  peribranchial  spaces, 
J.  Anat.  and  Phys.  xii,  232-236.  '89  GAGE,  S.  H.,  Blood,  P.  Am. 
S.  Micros,  x,  77-83,  and  J.  R.  M.  S.  494.  '17  HOME  (Gills),  Isis, 
25-35.  >93  HOWES,  G.  B.,  Abnormal  gill  clefts  in  Pet.  and  Myx.  P. 
Zool.  S.  730-733.  '87  JULIN,  CH.  (Two  anterior  gill  slits),  B.  Acad. 
Roy.  Sci.  Brux.  xiii,  275-293.  '88  Appareil  vasculaire,  Zool.  Anz. 
xi,  567-568.  '94  KERKALDY,  J.  W.,  Head-kidney  of  Myx.  Q.  J. 


2^6  FISHES,   LIVING  AND  FOSSIL 

M.  S.  353-359-  '90  KLINCKOWSTROM,  A.,  Darm-u.  Lebervenen 
b.  Myx.  Biol.  Foren.  62-67.  '93  KUPFFER,  C.  v.,  Pankreas,  SB. 
Morph.  Gesell.  Mun.  ix,  37-59.  '82  LEGOUIS,  P.  S.,  Pancreas, 
C.  R.  xcv,  305-308,  and  Ann.  S.  Sci.  Brux.  viii,  187-304.  '32 
MAYER,  C.,  milz.  Gror.  Nat.  xxxiv,  165-166.  '76  MEYER,  F., 
Nieren,  Centr.  f.  d.  medicin.  Wiss.  No.  2.  '39  MULLER,  J., 
Gefasse:  Wundernetze,  Monatsheft,  Berlin,  184-186,  and  272-292. 
'39  Lymphgefasse,  AH.  d.  Berl.  Akad.  '73  MULLER,  W., 
Urniere  b.  Myx.  Jen.  Z.  vii.  '75  Urogenital  system,  AH.  d. 
Ak.  d.  Wiss.  Berl.  ix.  '21  OKEN,  J.  (Gills),  Isis,  271-272,  and 
'29  VH.  Gesell.  Natur.  Berl.  1, 133-141.  '46  ROBIN,  C.,  Systeme 
veineux,  L'Inst.  xiv,  120-123.  '87  THOMPSON,  D'A.  W.,  Blood, 
Ann.  N.  H.  xx,  231-233,  and  Anat.  Anz.  ii,  630-632.  '84  WELDON, 
W.  F.,  Head-kidney  of  Bdell.  Q.  J.  M.  S.  xxiv,  171-182. 

NERVOUS  SYSTEM,  END  ORGANS.  — '82  AHLBORN,  F.,  Gott- 
ing.  Nachr.  677-682.  '83  Z.  wiss.  Zool.  xxxix,  191-294.  '84 
Hirnnerven,  Z.  wiss.  Zool.  xl,  286-308.  '88-'89  BEARD,  J., 
Parietal  eye,  Nature,  xxxvi,  246-298,  and  340-341,  also  Q.  J.  M.  S. 
xxix,  55-73.  '77  FREUD,  S.,  Nervenwurzeln  im  Riickenmark, 
SB.  Ak.  Wien,  Ixxv.  '78  Spinalganglien,  SB.  Ak.  Wien,  Ixxviii. 
'78  GOETTE,  A.,  Spinalganglien,  A.  mikr.  Anat.  xv,  332-338. 
'72  HASSE,  Auditory  organ,  Anat.  Studien,  I,  Heft  3,  and  Ketel, 
ibid.  489-541.  '79  JELENEF,  A.  (Cerebellum),  B.  Pdtersb.  xxv, 
333-345.  '86  JULIN,  C.  (Sympathetic),  A.  Zool.  exper.  vi,  and 
Anat.  Anz.  '87,  192-201.  '87  Nerfs  lateral,  B.  Acad.  R.  Brux. 
xiii,  300-309.  '92  KOHL,  C.,  D.  Auge  v.  Pet.  u.  Myx.  Leip. 
Reudnitz.  br.  '37  MULLER,  J.,  Gehb'rorgan,  Abh.  Berl.  Acad. 
'38  Nervensystem  d.  Myx.  Berl.  Monatsber,  16-20.  '85  NANSEN, 
F.,  Aarsber.  Berg.  Mus.  55-78  (trans,  in  Ann.  N.  H.  xviii, 
209-226.  '64  OWSJANNIKOW,  P.,  Gehb'r.  Me'm.  Acad.  St.  Pe'tersb. 
viii.  '83  (Sympathetic),  Arb.  Naturf.  Gesell.  xiv,  and  '84  B. 
Acad.  St.  Petersb.  xxviii,  439-448.  '88  (Pineal  eye),  Mem. 
Acad.  St.  Petersb.  xxxvi.  '86  RANSOM,  W.  and  THOMPSON,  D'A., 
Spinal  and  visceral  nerves,  Zool.  Anz.  ix,  421.  '80  RETZIUS, 
G.,  Riechepithel.  A.  f.  Anat.  u.  Phys.  '90  (Myxine :  caudal 
heart,  nerve  and  sub-cutaneous  ganglion  cells),  Biol.  Untersuch. 
Neue  Folge,  Stockholm,  Fol.  '92  Nervenendungen  in  der  Haut, 
des  Pet.,  op.  cit.  (2)  III,  37-40,  and  (tail  structures),  op.  cit.  iv, 
36-41.  '93  Gehirn-Auge  v.,  Myx.  op.  cit.  v,  27-30.  And 
Geschmacksknospen  bei  Pet.  op.  cit.,  69-70.  '82  ROHON,  J.  V., 
Ursprung  d.  acusticus.  SB.  Ak.  Wien,  Ixxxv,  245-267.  '84  SAC- 
CHI,  T.  (Neuroglia  of  retina),  Arch.  Ital.  Biol.  vi,  76-96. 


BIBLIOGRAPHY:    CYCLOSTOMES  237 

'80  SCHNEIDER,  A.,  Nerven,  Zool.  Anz.  330.  '71  SCHULTZE,  M., 
Retina,  SB.  nieder-rhein  Gesell.  6  Nov.  '79  SELENEFF,  A.  (Cere- 
bellum), B.  Acad.  St.  Petersb.  xxv,  333-343,  and  '80  Melanges 
Biol.  St.  Petersb.  x,  307-325.  '88  WHITWELL,  J.  R.,  Epiphysis, 
J.  Anat.  Phys.  xxii,  502-504.  '79  WIEDERSHEIM  (Brain  and 
nerves),  Zool.  Anz.  589-592  and  '80  in  Jen.  Z.  xiv,  1-24. 

EMBRYOLOGY. 

I.  General  '88  GOETTE,  A.,  Zool.  Anz.  xi,  160-163  and  '90  in  AH- 
3,  Entwicklungesch.  d.  Thiere,  5  Heft.  '88  KUPFFER,  C.  v.,  SB. 
bayer.  Akad.  I,  70-79,  and  '90  in  A.  mikr.  Anat.  xxxv,  469-558. 
'90  NESTLER,  Zool.  Anz.  xiii.  '81  NUEL,  J.  B.,  A.  d.  Biol.  i,  and 
'82  ii,  403-454;  also  J.  R.  M.  S.  ii,  26-27.  1<7°  OWSJANNIKOW,  B. 
Acad.  St.  Petersb.  xiv,  325  and  '89,  xxxii,  83-95,  and  '91  M£l. 
Biol.  xiii,  55-67  and  B.  Acad.  St.  Petersb.  13-55,  and  '93  Ann- 
N.  H.  xi,  30-43.  '81  SCOTT,  W.  B.,  O.  J.  M.  S.  xxi,  146-153,  Zool. 
Anz.  ('80)  422,  and  Morph.  JB.  vii.  Also  '82,  A.  Zool.  exper. 
ix,  and  (pituitary  body  and  teeth)  Science,  ii,  184-186,  731-732. 
Also  '88  J.  of  Morph.  i,  253-310.  '87  SHIPLEY,  A.  E.,  Q.  J.  M.  S. 
xxvii,  325-370,  and  A.  Zool.  expe'r.  i.  Also  Stud.  Morph.  Lab. 
Camb.  iii. 

II.  Ovary ',  Sperm,  Fertilization.     '93  BEARD,  J.,  Testes  with  ova, 
Anat.  Anz.  viii,  59-60.     '87  BOHM,  A.  A.,  Befruchtung,  SB.  bayer. 
Akad.  8  Feb.,  and  A.  mikr.  Anat.  xxxii.     '77  CALBERLA,  E., 
Befruchtungsvorgang.  Z.  wiss.  Zool.  xxx,  437-486.     '87  CUNNING- 
HAM, T.,  Ova  of  Bdell.  Tr.  Roy.  S.  Edinb.  xxx,  247-250,  (Myxine) 
Zool.    Anz.   390-392,  and  Q.  J.  M.  S.  xxvii,  49-76.     '91    Sper- 
matogenesis  of  Myx.  Q.  J.  M.  S.  xxxiii,  169-186,  and  Zool.  Anz. 
xiv,  22-27.     '83  FERRY,  L.  (Internal  fecundation),  CR.  Ixxxxvi, 
721-722,  and  Ann.  N.  H.  xi,  388.     '75  GULLIVER,  Spermatozoa, 
P.  Zool.  S.  336.     '78  KUPFFER,  C.  v.,  u.  BENECKE,  Befruchtung. 
Festschr.  Th.  Schwann  Kbnigsberg.     '86  NANSEN  (Protandric), 
Myxine,  Zool.  Anz.  676,  '87  in  Bergens  Mus.  Aarsber,  pp.  34,  and 
'89  (Q.  J.  M.  S.  188-189)  ZooL  Anz-  26r-     '8°  NUSSBAUM,  M. 
(Eggs  and  spawning),  A.  mikr.  Anat.  xviii,  1-121.     '89  RETZIUS, 
Entwick.  d.  Myx.  Biol.  For.  i,  22-28,  Anhang.  50-51  (Dec.  '88). 
'63  STEENSTRUP,  J.  (Egg  of  Myxine),  Oversigt.  o.  d.  K.  danske 
Videnskabernes     Selskabs    Forh.     233-239.      '87     WEBER,    M. 
(Reply  to  Cunningham),  Zool.  Anz.  318-321.   Geslachtsorganenv. 
Myx.  Ned.  Dierkd.  Vereen,  4  pp.  D.  I.  Afl.  3-4. 

III.  Organogeny.     '77  CALBERLA,  E.,  Medullarrohr,  Morph.  JB.  iii. 
'82  DOHRN,  Hypophysis,  Zool.  Anz.  587-588,  '83  in  MT.  z.  Stat. 
Neapel,    iv,    172-189.      '84   Visceralbogen,   op.    cit.  v,    152-189. 


FISHES,   LIVING  AND  FOSSIL 

'86  Thyreoidea,  op.  cit.  vi.  '87  (Thyroid,  Spiracle,  Pseudo- 
branch),  op.  cit.  vii,  301-337-  '88  Nerven  u.  Gefasse,  op.  cit.  viii, 
233.  '92  HATTA,  S.,  Germinal  Layers,  J.  Coll.  Sci.  Japan,  v, 
129-147.  '84  HERMS,  E.,  Nervus  acusticus,  SB.  math.  nat.  Acad. 
MUnch.  333-354-  '93  McCLURE,  Early  stages,  Zool.  Anz.  xvi, 
429.  '85  SHIPLEY,  A.  C.,  Mesoblast  and  blastopore,  P.  Roy.  S. 
Lond.  xxxix,  244-248.  '86  Nervous  system,  P.  Camb.  Phil.  S. 
v,  374-  '79  WIEDERSHEIM,  Brain  and  spinal  nerves,  Zool.  Anz. 
ii,  589-592- 

THE   OSTRACODERMS  AND   PAL^OSPONDYLUS 
(Cf.  SMITH  WOODWARD'S  Cat.  Foss.  Fishes.) 

'85  COPE,  E.  D.,  Position  of  Pterichthys,  Am.  Nat.  xix,  289-291. 
'92  CLAYPOLE,  E.  W.,  Pteraspidian  family,  Q.  J.  Geol.  S.  xlviii, 
542-562.  '90  PATTEN,  W.,  Q.  J.  M.  S.  xxxi,  359-365.  '94 
Limulus  and  Pteraspis,  Anat.  Anz.  '94  ROHON,  J.  V.  (Meta- 
merism of  Cephalaspids),  Zool.  Anz.  51.  '88  TRAQUAIR,  R.  H., 
Asterolepids,  Ann.  N.  H.  ii,  485-504,  and  ('89)  P.  Phys.  Soc. 
Edinb.  23-46.  '90  Palaeospondylus.  Ann.  N.  H.  vi,  485,  and 
'93  in  P.  Roy.  Phys.  Soc.  Edinb.  xii,  87-94,  and  '94  op.  cit.  xiir 
312-321.  '92  SMITH  WOODWARD,  Forerunners  of  Backboned 
Animals,  Nat.  Sci.  i,  596-602. 

THE   SHARKS 

GENERAL. —  '65  DUMERIL,  A,  Hist.  nat.  d.  poissons,  Tome  I 
(Sharks,  Skates,  and  Chimaera),  pp.  720,  Paris.  '79-'80  MIKLOUHO- 
MACLAY,  Plagiostomes  of  the  Pacific,  i,  ii,  iii  (Anat.  notes : 
Dentition  of  young  Cestracionts),  P.  Linn.  S.  N.  S.  Wales,  iiir 
306-326.  '41  MULLER,  u.  HENLE,  Syst.  Beschr.  d.  Plagiost. 
folio,  60  pis.  Berlin. 

ANATOMY,  GENERAL.  — '85  CARMAN,  Chlamydoselache,  B.  Mus. 
Comp.  Zool.  (cf.  Gunther  in  Challenger  report).  '90  JAEKEL, 
O.,  Kiemenstellung  u.  System,  d.  Sel.  (?)  Berlin.  '91  Pristi- 
ophorus,  A.  f.  Naturges,  15-48.  LEUCKART,  R.,  Bildung  d. 
Korpergestalt  b.  Rochen.  Z.  wiss.  Zool.  ii,  258.  '93  MAREY 
(Swimming  movements  of  Ray),  C.  R.,  cxvi,  77-81.  '92  MAR- 
SHALL and  HURST,  Practical  Zoology  (Dog-fish),  Putnam,  N.  Y. 
'84  PARKER,  T.  J.,  Zootomy  (Skate),  Macmillan.  '84  WILS, 
H.  B.,  Squatina.  Lugd.  Bat. 

SKELETON.— '85  DOHRN  (Visceral  arches  of  Skate),  MT.  z.  Stat. 


BIBLIOGRAPHY:  SHARKS 


239 


Neapel,  vi.  '72  GEGENBAUR,  Kopfskelet,  4to,  Leip.  '78  HASSE, 
C.  (Vertebrae,  Morph.  JB.  iv,  214-268,  and  op.  cit.  Supplt.  43-58, 
and  Berl.  Verb.  Naturw.  173-174  (Zool.  Anz.  i,  144-148  and  167- 
171).  Also  '85,  4to,  27  pp.  Leip.  '84  HASWELL,  W.  A.,  P.  Linn. 
S.  N.  S.  Wales,  ix,  71-117.  '78  HUBRECHT,  Bronn's  Klassen  u. 
Ordnungen.  '64  KOLLIKER,  Wirbel,  Senkenb.  Naturf.  Gesell.  v, 
51-99.  Also  4to.  Frankfurt.  '90  PARKER,  T.  J.,  Sternum  in 
Notidanus,  Nature,  xliii,  142.  '78  PARKER,  W.  K.,  Skull  (with 
develop.)  of  shark  and  skate,  Tr.  Zool.  S.  x,  184-234.  '84  ROSEN- 
BERG, E.,  Occiput,  Festschr.  Dorpat.  4to,  20  pp.  And  '87  in  SB. 
Gesell.  Dorp,  viii,  31-34.  '73  STEENSTRUP,  J.  (Gill  rakers  of 
Selache),  Overs.  Dan.  Selsk.  No.  i.  '90  WHITE,  P.  J.,  Skull  and 
vise,  skelet.  of  Laemargus,  Anat.  Anz.  v,  259-261. 

FINS  AND  GIRDLES.  — '81  BALFOUR,  Skates,  P.  Zool.  S.  '70 
GEGENBAUR,  Skel.  of,  Jen.  Z.  v,  397-447,  also  (claspers)  448-458. 
'90  HOWES,  Batoid  and  Squaloraja,  P.  Zool.  S.  675-688.  '85 
MAYER,  P.,  Unpaaren  Flos.  MT.  z.  Stat.  Neap,  vi,  217-285.  '79 
METSCHNIKOFF,  O.  (Morph.  of  girdles),  Z.  wiss.  Zool.  xxviii,  423- 
438.  '79  MIVART,  ST.  G.,  T.  Zool.  S.  x,  439-484.  '92  MOLLIER, 
S.  (Entwickelung),  Vorl.  MT.  Anat.  Anz.  vii,  351-365,  also  '77 
THACHER,  J.,  Tr.  Connec.  Acad.  iii. 

INTEGUMENT  AND  TEETH.  — '44  AGASSIZ,  L.,  Dents  et  rayons, 
4to,  Neuchatel.  '68  HANNOVER,  A.,  Ecailles.  (?).  HARLESS,  E., 
Zahnbau  v.  Myliobates,  4to  (?).  '74  HERTWIG,  O.  (also  develop- 
ment), Jen.  Z.  viii.  '72  RANVIER,  L.,  Etranglements  annulaire 
(Rays),  C.  R.  1129-1132. 

VISCERA,  VESSELS,  GLANDS.  — '92  ANTIPA,  G.,  Thymus,  Anat. 
Anz.  vii,  690-692.  '88  AYRES,  H.,  Carotids  (Chlamydosel.)»  B. 
Mus.  Comp.  Zool.  xvii,  191-224.  '78  BLANCHARD,  R.,  Superanal 
gland,  J.  de  1'Anat.  Phys.  xiv,  442-450,  and  B.  S.  Zool.  Fr.  vii, 
399-401.  '79  BRIDGE,  Pori  abdominales,  J.  Anat.  Phys.  '82 
DROSCHER,  W.  (Histol.  of  gills),  A.  f.  Nat.  xlviii,  120-177.  '90 
EWART,  J.  C.,  Spiracle  of  Lamna,  J.  Anat.  Phys.  xxiv,  227-229. 
'78  FURBRINGER,  Excretory  system,  Morph.  JB,  49-56.  '91 
GEGENBAUR,  Cb'calanhange  v.  Mitteldarm,  Jen.  Z.  (?),  180-184. 
'90  HOWES,  Kidney  of  Raja,  J.  Anat.  Phys.  xxiv,  407-422.  '90 
Visceral  anat.  of  Hypnos,  P.  Zool.  S.  669-675.  '72  HYRTL,  J., 
Kopfarterien,  DS.  Ak.  Wiss.  Wien,  xxxii,  263-275.  '85  LIST, 
J.  H.,  Cloakenepithel,  SB.  Akad.  Wien  (?),  and  Anat.  Anz.  vii, 
545-546.  '80  PARKER,  T.  J.,  Spiral  valve  of  Ray,  T.  Zool.  S.  xi, 
49-61,  and  Venous  system,  Tr.  N.  Zeal.  Ins.  xiii,  413-418.  '86 
On  the  vessels  of  Mustelus,  and  ('87)  on  Carcharodon,  P.  Zool. 


FISHES,  LIVING  AND  FOSSIL 

S.  (?).  '90  PILLIET,  A.  (Histol.  of  liver),  C.  R.  Soc.  Biol.  ii, 
690-694.  '82  POUCHET,  G.,  Termin.  vascul.  d.  la  Rate,  J.  de 
1'Anat.  Phys.  xviii,  498-502.  '88  RUCKERT,  J.,  Excretions-organe, 
A.  Anat.  Phys.  (Anat.),  205-278.  '77  STOHR  (Valves  in  arterial 
conus),  Morph.  JB.  ii,  197-228.  '79  TROIS,  E.  F.  (Carotids  of 
Oxyrhina),  Atti  del  Inst.  Ven.  and  '83  (Of  Alopecias),  op.  cit. 
'73  TURNER,  W.,  Visceral  Anat.  of  Laemargus,  J.  Anat.  Phys. 
233.  '75  Spiny  Shark,  op.  cit.  '79  Pori  abdominales,  op.  cit. 
xiv,  1 01-102.  '81  Teeth  and  gill-rakers  of  Selache,  op.  cit.  xiv, 
273-286.  '93  VIRCHOW,  H.,  Spritzlochkieme,  SB.  Gesell.  n. 
Freunde,  Berl.  177-182;  Augengefasse  ('90)  A.  Anat.  Phys. 
(Phys.),  169-173.  '67  MIKLUCHO-MACLAY,  Schwimmblasenrudi- 
ment,  Jen.  Z.  iii,  448-453. 

NERVOUS  SYSTEM  AND  END  ORGANS.  — '92  BRAUS,  H., 
Rami  ventrales  d.  vord.  Spinalnerven.  Inaug.  Diss.  35  pp.  Jena. 
'83  CATTIE,  J.  F.,  Epiphysis,  Z.  wiss.  Zool.  xxxix,  720-722,  and 
A.  Biol.  iii,  101-196.  '90  CHEVREL,  R.,  Sympathetic,  A.  Zool. 
exper.  v,  196  pp.  '91  COGGI,  A.,  Vdsicules  de  Savi  (Torpedo), 
A.  Ital.  Biol.  xvi,  216-224.  '92  EDINGER,  L.,  Zwischenhirn,  AH. 
Senck.  Gesell.  xviii,  55  pp.  (and  Anat.  Anz.  vii,  472-476).  '78 
EHLERS,  E.,  Gehirn  u.  Epiphyse,  Z.  wiss.  Zool.  xxx,  Suppl.  607. 
'90  EWART,  J.  C.,  Cran.  nerves  of  Torpedo,  P.  Roy.  S.  xlvii, 
240-291.  '92  Electric  organ  of  Skate,  Phil.  Trans,  clxxxiii, 
389-420  (Abs.  in  P.  Roy.  S.  474-476).  '92  Sensory  canals  of 
Laemargus,  and  Skate,  Tr.  Roy.  S.  Edinb.  Nos.  5-6  (Abs.  in 
Zool.  Anz.  xv),  116-120.  '88  FRITSCH,G.,  Bedeuting  d.  Kanalsyst 
SB.  Ak.  Berl.  273-306.  '88-'89  GARMAN,  Lateral  line  (figures 
many  forms),  B.  Mus.  Comp.  Zool.  xvii,  No.  2.  '71  GEGENBAUR, 
Kopfnerven  v.  Hexanchus,  Jen.  Z.  497-560.  '75  JACKSON,  W.  H., 
and  CLARKE,  Brain  and  nerves,  J.  Anat.  Phys.  x,  75-197.  '87 
LEGER,  M.,  Cervelet  d'un  Alopias,  B.  S.  Philom.  xi,  160-163. 
'81  MARSHALL,  A.  M.,  Head  cavities  and  nerves,  Q.  J.  M.  S.  xxi, 
72,  and  (with  SPENCER)  469-499.  '80  MERKEL,  Sens,  nerven  in 
d.  Haut.  Rostock.  '70  MIKLUCHO-MACLAY,  Gehirn,  4to,  74  pp. 
Leip.  '78  RETZIUS,  G.,  Memb.  Gehorlabyr.  A.  Anat.  Phys. 
(Anat.),  83-105.  '91  REX,  H.  (Morph.  of  cran.  nerves),  Morph. 
JB.  xvii,  417-466.  '78  ROHON,  J.  (Brain),  DS.  Ak.  Wien,  xxxviii, 
43-108.  '86  SANDERS,  A.,  Phil.  Trans,  clxxvii,  733-764,  and  P. 
R.  S.  xl.  '89  SHORE,  T.  W.,  Vagus,  J.  Anat.  Phys.  iii,  428-451. 
'80  SOLGER  (Organs  of  lateral  line),  A.  mikr.  Anat.  xvii.  '73 
STIEDA,  L.,  Riickenmark,  Z.  wiss.  Zool.  xxiii,  435-442.  '73 
TODARO,  F.  (Gustatory  buds  and  branch,  membr.),  Recherche 


BIBLIOGRAPHY:   SHARKS  241 

lab.  univers.  Roma.  (Abs.  in  A.  Zool.  expdr.)  534-558.  '91 
VALENTI,  G.,  Histogenesis,  A.  Ital.  Biol.  xvi,  247-252.  '76 
VIAULT,  F.,  Histology,  A.  Zool.  exper.  v,  441-528.  '83  VIGNAL, 
Sys.  ganglionaire  (Ray),  op.  cit.  i,  xvii. 

EMBRYOLOGY,  GENERAL.  — '76  BALFOUR,  G.  M.,  in  Q.  J.  M.  S. 
xiv,  and  Camb.  J.  Anat.  Phys.  xi,  pt.  I.  Also  '78  Monograph, 
Macmillan,  London.  '90  BEARD,  J.,  Skate,  R.  Fish.  Board,  Edin. 
'89  EIGENMANN,  C.  H.  and  R.  S.,  Young  stages,  West  Am. 
Nat.  vi,  150-151.  '85  HASWELL,  W.  A.,  Young  Pristiophorus,  P. 
Linn.  S.  N.  S.  Wales,  ix,  680-681.  '77  His,  W.,  Ueb.  d.  Bildung 
v.  Haifishembryonen,  Z.  wiss.  Zool.  ii,  108-124.  '81  HOFFMANN, 
C.  K.  (?),  Harlem.  '88  KASTSCHENKO,  N.,  Anat.  Anz.  iii,  445- 
467.  '70  KOWALEWSKY,  A.  (Russian),  Trans.  Kiew.  Soc.  of 
Nat.  i.  '52  LEYDIG,  F.,  Mikr.  Rochen  u.  Haie,  Leip.  Englemann, 
iv,  127  pp.  '76  MALM,  A.  W.,  Kongl.  vet.  akad.  forhand.  Stock- 
holm. '42  MULLER,  J.  (Emb.  differences  of  Shark  and  Ray), 
fol.  Berlin.  '86  PERENYI,  J.,  Torpedo,  Zool.  Anz.  ix,  No.  227, 
433-436.  '77  SCHULTZ,  A.,  A.  mikr.  Anat.  '92  SEDGWICK,  A., 
Q.  J.  M.  S.  xxxiii,  559-586.  '64,  WYMAN,  Raja,  Mem.  Am.  Acad. 
Arts  and  Sciences,  ix. 

I.  Breeding,    Gestation.  —  '73    AGASSIZ,    A.,    P.     Bost.     Soc.     xiv, 

339.  '90  ALCOCK,  A.,  J.  A.  Soc.  Bombay,  lix,  51-56.  (Of 
Rays)  '92  Ann.  N.  H.  ix,  417-427,  and  x,  1-8.  '79  BOLAU,  H. 
(Of  Scyllium),  VH.  Ver.  Hamb.  iii,  122-130  and  ('81)  Z.  wiss. 
Zool.  xxxv.  '67  COSTE  (Of  Scyllium),  C.  R.  99-100,  and  Ann. 

M.  N.  H.  xix,  227.      '70  HOME,  E.,  Ovoviviparous  Sharks. 

'68  MACDONALD,  J.  D.,  and  BARRON,  CH.,  Heptanchus,  P.  Zool.  S. 
37!-373-  '85  MATTHEWS,  J.  D.,  Oviduct  of  Skate,  J.  Anat.  Phys. 
xix,  144-149.  '90  MEHRDORF,  C.  (Gestation),  Rostock,  51  pp. 
'72  MEYER  (Scyllium),  Zool.  Gait.  371.  '85  OERLEY,  L. 
(Gestation),  Term,  fiizetek.  ix,  293-309.  '90  PARKER,  T.  J., 
Mustelus,  Tr.  N.  Zeal.  Inst.  xxii,  331-333.  '77  PETRI,  K.  R., 
Copulationsorgane,  Z.  wiss.  Zool.  xxx,  288-385.  '75  SCHENK, 
S.  L.,  Kiemenfader,  SB.  Akad.  Wien.  12  pp.  '79  SCHMIDTLEIN,  R., 
MT.  z.  Stat.  Neap.  1,  61.  '91  WOOD-MASON  and  ALCOCK,  Gesta- 
tion of  Pteroplataea,  P.  Roy.  S.  xlix,  359-367,  and  1,  202-209. 
'67  TROIS,  E.  F.  (Acanthias'  gestation),  Atti.  Inst.  Ven.  171-176. 
'77  (Gestation  of  Myliobatis  and  Centrina),  op.  cit.  ii,  429. 
'77  TURNER,  W.,  Laemargus'  oviducts,  J.  Anat.  Phys.  xii,  604- 
607,  and  ('85)  op.  cit.  xix,  221-222. 

II.  Egg,    Gastr tdation.  —  '92   DOHRN,   Schwann'schen   Kerne,   Anat. 
Anz.  vii,  348-351.      '72  GERBE,  Z.,  Segmentation,  J.  de  1'Anat. 

R 


FISHES,   LIVING  AND  FOSSIL 

Phys.  181  HERRMANN,  G.,  Spermatogenese,  C.  R.  xciii,  858-860, 
and  '83  J.  1'Anat.  Phys.  xviii,  373-432.  '83  HERTWIG,  O. 
(Middle  germ  layer),  Jen.  Z.  xvi,  287-290.  '83  HOFFMANN,  C.  K. 
(Middle  germ  layer),  Arch.  Neerland.  xviii,  241.  '92  Endothelial 
Anlage  d.  Herzens,  Anat.  Anz.  vii,  270-273,  and  '93  in  Morph. 
JB.  xix,  592-648.  '88  KASTSCHENKO,  Dotterkerne,  Anat.  Anz. 
'90  (Early  develop,  and  muscles),  Zool.  Beitr.  ii,  251-266.  '86 
KOLLMANN,  Furchung  (C.  R.  '84),  Congr.  pe'r.  internal,  d.  sc. 
mdd.  Copenhague,  i,  Sect.  d'Anat.  50-52,  and  VH.  d.  Natur. 
Gesell.  Basle,  Th.  viii,  Heft  i.  '78  LA  VALLETTE,  ST.  GEORGE,  A., 
Spermatosomatum,  Bonn,  4to,  9  pp.  '79  LUTKEN,  Laemargus' 
eggs,  oviduct,  Vid.  Medd.  ('80)  56-61.  '84  PERRAVEX,  M.  E. 
(Egg  case),  C.  R.  xcix,  1080-1082.  '89  OSTROUMOFF,  A.,  Blasto- 
porus  u.  Schwanzdarm,  Zool.  Anz.  xii,  364-366.  '85  RUCKERT,  J., 
Keimblattbildung,  SB.  Gesell.  Morph.  MUnchen,  i,  48-104,  and 
'89  in  Anat.  Anz.  iv,  353-374.  '86  Gastrulation  (and  middle 
germ  layer),  Anat.  Anz.  286-287,  and  '87  op.  cit.  97-112  and 
151-174.  '91  Befruchtung,  Anat.  Anz.  vi,  308-322.  '92  Ova- 
rialei,  vii,  107-158,  Chromosomen,  viii,  44-52.  '86  RYDER, 
Segmentation,  Am.  Nat.  xx,  470-473,  and  B.  U.  S.  F  C.  8-10. 
'82  SABATIER,  A.,  Spermatogenese,  C.  R.  xciv,  1097-1099.  '75 
SCHULTZ,  A.  (Ovogenesis),  A.  mikr.  Anat.  xi,  569-582.  '73 
SCHENK,  S.  L.  (Egg  and  oviduct),  SB.  Akad.  Wien,  Ixxiii. 
74  Dotterstrang,  op.  cit.  Ixix,  301-308.  '90  SCHNEIDER,  A. 
(Gastrula-muscles),  Zool.  Beitr.  ii,  251-266.  '85  SWAEN,  A. 
(Germ  layers  and  blood),  B.  Acad.  roy.  Belgique,  ix,  and  '86  in 
A.  de  Biol.  vii,  537-585.  '83  TROIS,  E.  F.,  Spermatozoi,  Atti.  Inst. 
Ven.  and  J.  Microgr.  vii,  193-196.  '84  VAILLANT,  L.,  Orientation 
des  oeufs  dans  1'ute'rus,  B.  Soc.  Philom.  viii,  178-179.  '88  ZIEGLER 
(Mesenchyme),  A.  mikr.  Anat.  xxxii.  '92  ZIEGLER,  H.  E.  and  F. 
(Early  development),  A.  mikr.  Anat.  xxxix,  56-102. 

III.  Integument,  Skeleton.  —  '81  BENDA,  C.,  Dentinbildung,  A.  mikr. 
Anat.   xx,    246-270.      '79   HASSE,  C.,   Knorpel,  Zool.   Anz.   ii, 
325-329,    351-355,  and  371-374-     '82   Wirbelsaule,   Jena  ('79), 
4to.     '92  Wirbelsaule,  Z.  wiss.  Zool.  Iv,  519-531.     '60  KOLLIKER, 
A.,  Chorda  u.  Wirbel.  Wiirz.      '87  PERENYI,  J.,  Chorda,   peri- 
chordal.  Math.  u.   Naturwiss.  Ber.  a.  Ungarn,  iv,  214-217,  and 
('89)  in  218-241.     '93   PLATT,  JULIA  B.,  Ectodermic  cartilage, 
Anat.  Anz.  506.     '78  REICHERT,  Vordere  Ende  d.  Chorda,  AH. 
Ak.  Berl.  49-1 13.    '84  ROSENBERG,  E.,  Occipitalregion,  Festschrift, 
Dorpat,  26  pp.  4to. 

IV.  Viscera.  —  '87  BEARD,  J.,  Segmental  duct,  Anat.  Anz.  ii,  646-652. 


BIBLIOGRAPHY:   SHARKS 


243 


'85  BEMMELEN,  J.  F.  v.  (Rudimentary  gill  slits),  MT.  z.  Stat. 
Neap,  vi,  165-184.  '79  BLANCHARD,  R.,  Fingerformigen  Driise, 
MT.  Emb.  Inst.  Schenk,  iii,  179-192,  and  ('77)  J.  de  1'Anat.  xlv, 
442-450.  '84  DOHRN,  Kiemenbogen,  Flossen,  MT.  z.  Stat.  Neap. 
v,  102-189.  '87  MAYER,  P.  (Circulatory),  op.  cit.  vii,  338-370, 
and  ('88)  viii,  307-373.  Also  Anat.  Anz.  ix,  185-192.  '77 
MAYER,  F.,  Urogenitalsys.  SB.  Gesell.  Leip.  ('76),  38-44.  '92 
RABL,  C.,  Venensys.  Leuckart  Festschr.  228-235.  '92  RAF- 
FAELE,  F.,  Sist.  vascolare,  MT.  z.  Stat.  Neap,  x,  441-479.  '88 
RUCKERT,  J.,  Endothel.  Anlagen  d.  Herzens,  Biol.  Centralbl. 
viii.  '89  Excretionssys.  Zool.  Anz.  xii,  15-22.  '75  SEIKPER,  C., 
Urogenitalsys.  Arb.  a.  d.  Zool.  Zoot.  Inst.  Wiirz.  ii.  '88  WIJHE, 
J.  W.  v.,  Excretionsorgane,  Zool.  Anz.  xi,  539-540,  and  Anat. 
Anz.  iii,  74-76,  and  '89  in  A.  mikr.  Anat.  xxxiii,  461-516. 

V.  Nervous  System  and  End  Organs.  —  '85  BEARD,  J.,  Cranial 
ganglia,  Zool.  Anz.  viii,  220-223,  Anat.  Anz.  iii,  874-905,  and 
op.  cit.  '92,  191-206.  '91  KILLIAN,  Metamerie,  VH.  Anat. 
Gesell.  85-107.  '88  DOHRN  (Motor  fibres),  MT.  z.  Stat.  Neap. 
viii,  441-462.  '91  Augenmuskelnerven,  op.  cit.  x,  1-40.  '91 
FRORIEP,  Kopfnerven,  VH.  Anat.  Gesell.  55-65.  '92  LENHOSSEK, 
M.  v.  (Spinal  ganglia  and  cord),  Anat.  Anz.  vii,  519-539.  '85 
ONODI,  A.  (Nerve  roots),  Ber.  Math.  Nat.  Ungarn,  ii,  310-336. 
'89  OSTROUMOFF,  A.,  Froriep'schen  Ganglien,  Zool.  Anz.  xii, 
363-364.  '90  PLATT,  J.  B.,  Anterior  head  cavities,  Zool.  Anz.  xiii, 
239,  and  '91  J.  of  Morph.  v,  79-106,  and  Anat.  Anz.  vi,  251-265. 
'96  PUNIS,  G.  C.,  Pineal  eye,  P.  Phys.  Soc.  Edinb.  62-67.  '92 
RABL,  C.,  Metamerie,  VH.  Anat.  Gesell.  104-135.  '80  RABL- 
RUCKHARDT  (Metamerism),  Morph.  JB.  vi,  535-570.  '93  Lobus 
olf.  impar.  Anat.  Anz.  Sep.  15.  '83  VIGNAL,  W.,  Systeme  gang- 
lionaire,  A.  Zool.  exper.  i,  17-20.  '83  VAN  WIJHE  (Metamerism), 
VH.  Aka£.  Wiss.  Amsterdam.  '76  WILDER,  B.  G.,  Anterior 
brain  mass,  Am.  J.  Sci.  xii,  103-106. 

MORPHOLOGY  OF  FOSSIL  SHARKS.  — V.  ref.  in  S.  Wood- 
ward's Catalogue,  also  in  present  writer's  article  on  Cladoselache, 
'94  J.  of  Morph.  ix,  112.  In  addition,  '88  BROGNIART  ET  SAUVAGE, 
Etudes  sur  le  Terrain  Houiller  de  Commentry,  Liv.  iii,  B.  de  la 
S.  d.  1' Indus,  miner,  ii.  1-39.  '93  CLAYPOLE,  E.  W.,  Cladodonts, 
Am.  Geol.  325-331,  and  ('95)  op.  cit.  Jan.  '93  COPE,  Clado- 
donts, Am.  Nat.  Sept.  Also  '94  J.  Am.  N.  S.  Phila.  ix,  427-441. 
'92-'94  DAVIS,  J.  W.,  Pleuracanths,  Acanthodians,  Tr.  Dub.  Roy. 
S.  '94  DEAN,  B.,  Cladodont,  Tr.  N.  Y.  Acad.  Sci.  115-119.  '92 
JAEKEL,  O.  (Eocene  sharks),  SB.  Gesell.  Nat.  Fr.  Berlin,  p.  6i> 


FISHES,  LIVING  AND  FOSSIL 

and  Cladodus,  I.e.  156-158.     '95   SMITH  WOODWARD,  Primaeval 

sharks,  Nat.  Sci.  vi,  38-44. 

THE   CHIMLEROIDS 
(Cf.  esp.  DUMERIL,  Ref.  p.  238.) 

'94  BEAN,  T.  H.,  Harriotta,  P.  U.  S.  Nat.  Mus.  xvii,  471-473.  '52 
COSTA  (Anatomy),  Faun,  regno  Napoli.  '51  LEYDIG,  F.,  Anat. 
and  Hist.  Mill.  A.  f.  Anat.  Phys.  xviii,  241-271.  '76  HUBRECHT, 
A.,  Kopfskelet,  Nied.  A.  Zool.  iii,  255-276,  and  '77  in  Morph.  JB. 
iii,  280-282.  '86  PARKER,  T.  J.,  Claspers  of  Callorhynchus,  Nat. 
xxxix,  635.  '75  SOLGER,  B.  (Visceral  skeleton),  Morph.  JB.  I, 
H.  I.  '37  DUVERNOY,  G.  Z.  (Heart  and  vessels),  Ann.  d.  Sc. 
Nat.  1-16.  '78  LANKESTER,  E.  R.,  Heart,  P.  Zool.  S.  634,  and 
'79  in  Tr.  Zool.  S.  x,  493-506.  '42  MULLER,  J.  (Nerves  and 
heart,  critique  of  Valentin),  A.  f.  Anat.  ('43)  ccliii.  '89  CARMAN, 
S.,  Lateral  line,  Mus.  Comp.  Zool.  xvii.  '70  MIKLUCHO-MACLAY 
(Brain),  Jen.  Z.  v,  132.  '79  SOLGER,  B.  (Lateral  line),  A.  mikr. 
Anat.  xvii,  95-113.  '42  VALENTIN  (Brain  and  Nebenherzen),  A. 
mikr.  Anat.  25-45.  '77  WILDER,  Brain,  P.  Philadel.  Acad.  Sci. 
219-250.  '90  ALCOCK,  Egg  capsule  of  Callorhynchus,  Ann.  N.  H. 
viii,  22.  '71  CUNNINGHAM,  Callorhynchus'  egg,  Notes  on  the 
N.  H.  of  the  Straits  of  Magellan,  340.  '89  GUNTHER,  Chimaera's 
egg,  A.  N.  H.  iv,  275-280. 

For  literature  of  Fossil  Chimaeroids  v.   SMITH  WOODWARD'S 
Catalogue. 

THE   LUNG-FISHES 

GENERAL  (NATURAL  HISTORY).  — '94  BOHLS,  Fang  u.  Lebens- 
weisev.  Lepidosiren.  Nachr.  Gesell.  Gottingen,  80-83.  '76  CAS- 
TLENAU,  F.,  Ceratodus,  C.  R.  Ixxxiii,  1034.  '92  DUBOIS,  R.> 
Respiration,  "hibernation,"  Ann.  S.  Linn.  Lyon,  xxxix,  65-72. 
'66  DUMERIL,  A.  M.  C.,  C.  R.  97-100,  and  Ann.  N.  H.  xvii,  160. 
'70  (Swim-bladder,  etc.),  Angers  ?  '94  EHLERS,  E.,  Lepid,  n.  s. 
Nachr.  Gesell.  Gottingen.  FRITSCH,  A.  (Living  and  Fossil  Lung- 
fishes  and  their  affinities),  Prag.  4to.  '87  GIGLIOLI  (Rediscovery 
of  Lepidosiren),  Nat.  xxxv,  343,  and  '88,  Nat.  xxxviii,  112. 
'56  GRAY,  J.  E.,  "  Lepidosiren,"  P.  Zool.  S.  Lon.  342.  '88  HOWES, 
Rediscovery  of  Lep.  Nat.  xxxviii,  126.  '41  JARDINE,  W.,  Ann. 
N.  H.  vii,  24.  '64  KRAUSS,  F.,  Protopterus,  Wiirt.  nYrwiss. 
Jahresber.  126-133.  '70  KREFFT,  Ceratodus,  P.  Zool.  S.  221- 


BIBLIOGRAPHY:  LUNG-FISHES  245 

224,  and  Ann.  N.  H.  221-224,  and  ('71)  P.  Roy.  S.  377. 
'91  LACHMAN,  H.,  Protop.  Zool.  Gart.  xxxii,  129.  '73  MARNO, 
E.,  Protop.  Zool.  Gart.  44.  '58-'59  MCDONNELL,  R.,  Protop.  Z. 
\viss.  Zool.x.  '37  NATTERER,  J.,  Lepid.  Ann.  Wien.  Mus.  II. 
'94  NATURAL  SCIENCE,  Lepid.  324-325.  '39-'41  OWEN,  Lepi- 
dosiren  annectans,  Tr.  Linn.  S.  xviii.  '45  PETERS,  W.,  Protop. 
Mill.  A.  '76  RAMSEY,  E.  P.,  Cerat.  P.  Zool.  S.  698.  SCHMELTZ, 
Cerat.  J.  Mus.  Godeffr.  viii,  138.  '66  SCLATER  and  BATES,  Lepid. 
P.  Zool.  S.  34.  '92  SPENCER,  W.  B.,  Cerat.  Viet.  Natural.  Melb. 
June  10,  and  P.  Roy.  S.  Viet,  iv,  81-84.  '89  STUHLMAN,  F., 
Cerat.  SB.  Akad.  Wiss.  BerL  32.  '87  WIEDERSHEIM,  Protop. 
Anat.  Anz.  ii,  707-713,  and  R.  Br.  Ass.  738-740. 

ANATOMY,  GENERAL.  — '85  AYERS,  H.,  Jen.  Z.  Naturwiss.  xviii, 
479-527.  '87  BAUR,  G.,  Lepid.  Zool.  JB.  ii,  575.  '4O  BISCHOFF, 
T.,  Lepid.  Leip.  '71  GUNTHER,  Ceratodus,  Ann.  N.  H.  vii,  227 
and  Phil.  Trans.  ('72)  clxi,  511-571,  and  P.  Roy.  S.  377-379, 
Nat.  Nos.  99,  100,  102.  '76  HUXLEY,  Ceratodus,  P.  Zool.  S. 
24-58.  '64  KLEIN,  Protop.  Wiirt.  n't'rwiss.  Jahresber.  134-144. 
'78  MIALL,  L.,  Cerat.  and  Protop.  Palaeont.  S.  xxxii,  1-32.  '88 
PARKER,  W.  N.,  Ber.  d.  Naturforsch.  Gesell.  Friburg,  VB.  iv,  H. 
3,  Nat.  xxxix,  9-21,  and  Tr.  Cardiff  Nat.  S.  xx.  '91  Protop. 
P.  Roy.  S.  xlix,  549-554.  '92  Protop.  (Large  memoir),  Tr.  R. 
Irish  Acad.  xxx,  115-227.  '66  PETERS,  Monatsber.  Ak.  Wiss. 
Berl.  12-13. 

SKELETON.  — '93  KLAATSCH,  H.,  Wirbel,  VH.  Anat.  Gesell,  130- 
132.  '91  TELLER,  F.,  Skull  of  Ceratodus,  AH.  Geol.  Reichanst. 
xv,  H.  3. 

MUSCLES.  —  '72  HUMPHREY,  G.  M.,  Ceratodus  and  Protop.  J.  Anat. 
and  Phys.  vi. 

FINS  AND  GIRDLES.  — '86  ALBRECHT,  P.,  Protop.  Fin  forked,  SB. 
Ak.  Berl.  545-546.  '91  BOULENGER,  Protop.  Renewed  pectoral. 
'83  DAVIDOFF,  M.,  Cerat.  Pelvic  fin.  '84  GILL,  T.,  Shoulder 
girdle,  Ann.  N.  H.  xi,  173-178.  '83  HASWELL,  W.  A.,  Cerat. 
Paired  fins,  P.  Linn.  S.  N.  S.  Wales,  vii,  2-11.  '91  HOPLEY,  C., 
Protop.  Renewed  pectoral,  Am.  Nat.  xxv,  487.  '87  HOWES,  G. 
B.,  Cerat.  Paired  fins  compared  with  sharks',  P.  Zool.  S.  3. 
'94  LANKESTER,  E.  Ray,  Lepid.  Villous  processes  of  hind  limbs, 
Nat.  Apr.  12.  '86  SCHNEIDER,  A.,  Zool.  Anz.  ix,  521-524,  and 
('87)  Zool.  Beitr.  ii,  97-105.  '71  TRAQUAIR,  R.  H.,  Protop.  Tail 
restored,  Br.  Ass.  R.  '90  VANHOFFEN,  Cerat.  VH.  Gesell.  D. 
Naturf.  ii,  134, 


246 


FISHES,   LIVING  AND  FOSSIL 


INTEGUMENT  AND  TEETH.  — '87  BOCKLEN,  H.,  Cerat.  Denti- 
tion, JH.  Ver.  Wiirt.  xliii,  76-81.  '60-'61  KOLLIKER,  A.,  Protop. 
Histol.  of  Skin,  Z.  Naturwiss.  Wiirzb.  i.  '65  PAULSON,  M., 
Protop.  Histol.  of  epidermis,  B.  Acad.  Sci.  St.  Pe'tersb.  viii, 
141-145.  '92  ROSE,  C.,  Zahnbau  u.  Zahnwechsel,  Anat.  Anz.  vii, 
821-839.  '89  WALTHER,  G.,  Prot.  Skin,  Z.  f.  Phys.  Chem.  xiii, 
H.  5.  '80  WIEDERSHEIM,  R.,  Scales,  A.  mikr.  Anat.  xviii. 

VISCERA,  VESSELS,  GLANDS.  — '80  BOAS,  E.  V.  (Heart  and 
arteries),  Morph.  JB.  vii,  32I-354-  1§78  FURBRINGER  (Excretory), 
Morph.  JB.  iv,  60.  '76  HUXLEY,  Anterior  nares,  P.  Zool.  S. 
180.  '45  HYRTL,  J.,  Lepid.  AH.  d.  bohm  Gesell.  Prag.  '78 
LANKESTER,  E.  R.,  Heart,  P.  Zool.  S.  634,  and  ('79)  Tr.  Zool.  S. 
x,  493-506.  '89  PARKER,  W.  N.,  Veins  (L.  cardinal),  P.  Zool.  S. 
145-151.  '94  SPENCER,  W.  B.,  Cerat.  Vessels  (complete  memoir), 
Macleay  Mem.  Vol.  Linn.  S.  N.  S.  Wales,  2-32. 

NERVOUS  SYSTEM,  END  ORGANS.  — '82  BEAUREGARD,  H. 
(Cranial),  J.  de  TAnat.  Phys.  xvii,  230-242.  '91  BURCKHARDT, 
R.,  Zirbel.  Anat.  Anz.  vi,  348-349.  '92  Cent.  nerv.  sys.  Berlin, 
64  pp.  Also  Zool.  Gesell.  ii,  92-95,  and  SB.  Nat.  Fr.  Berl. 
23-25.  '94  (Zwischenhirndach),  Anat.  Anz.  152.  '86  FUL- 
LIQUET,  G.  (Brain),  A.  Sci.  Naturelles,  xv,  94-96,  and  Rec. 
Zool.  Suisse,  iii,  1-130.  '94  PINKUS,  F.  (Undescribed  nerve), 
Anat.  Anz.  ix,  562-566,  and  (Cranial  nerves  of  Protop.)  Morph. 
Arb.  (Schwalbe),  275-346.  '89  SANDERS,  A.,  Cent.  nerv.  sys. 
Cerat.  Ann.  N.  H.  iii,  157-188.  '80  WIEDERSHEIM,  Skel.  and 
cent.  nerv.  sys.  Jen.  Z.  xiv,  and  Morph.  Stud.  Heft  i,  Jena.  '82 
WIJHE,  J.  W.  van,  Visceralskel.  u.  d.  Nerven.  Cerat.  Nied.  A. 
Zool.  v,  207-320.  '87  WILDER,  B.,  Brain,  Am.  Nat.  xxi,  544-548. 

EMBRYOLOGY.  — '86  BEDDARD,  F.  E.,  Ovarian  ovum,  P.  Zool.  S. 
272-292,  and  Zool.  Anz.  ix,  635-637.  '84  CALDWELL,  W.  H., 
(Preliminary),  J.  and  P.  Roy.  S.  N.  S.  W.  xviii,  and  ('87)  in  Phil. 
Trans,  clxxviii.  '93  HASSE,  C.,  Wirbelsaule,  Z.  wiss.  Zool.  Iv, 
533-542.  '93  SEMON,  R.  (Habits  and  development  —  surface 
views  of  eggs  and  larvae),  DS.  d.  Med.  Nat.  Gesell.  Z.  Jena,  pp.  50. 

THE   GANOIDS 

GENERAL  (NATURAL  HISTORY).  — '70  DUMERIL,  Aug.  Tome 
ii,  pp.  625,  Roret,  Paris.  '35  HECKEL,  J.,  Scaphirhynchus,  SB. 
Akad.  Wien.  '71  LUTKEN  (Classification),  Transl.  in  Ann.  N.  H. 
329-339.  '85  ORR,  H.  (Phylogeny)  Inaug.  Dissert.  Jena,  37  pp. 
'65-'66  SMITH,  J.  A.,  Calamoichthys,  P.  Roy.  S.  Edinb.  v,  654- 


BIBLIOGRAPHY:    GANOIDS  247 

659,  and  ('66)  457-479.     '69  STEINDACHNER,  F.,  Polypterus,  SB. 
Wien.  Akad.  Ix. 

GENERAL  ANATOMY.  — '87  TWANZOW,  N.,  Scaphirhynchus,  B. 
S.  Mosc.  1-41.  '54  LEYDIG  (Histology  of  Polypterus),  Z.  wiss. 
Zool.  v.  '50  LITTANY,  M.,  Acipenser,  B.  S.  Mosc.  xxiii,  389-445. 
'44  MULLER,  J.,  Bau  u.  Grenzen,  A.  f.  Anat.  and  ('46)  AH.  d. 
Berl.  Akad.  d.  Wiss.  '92  POLLARD,  H.  B.,  Polypterus,  Anat.  and 
phylogeny,  Morph.  JB.  V,  387-428,  and  preliminary  in  ('91) 
Anat.  Anz.  vi,  338-343.  '48  WAGNER,  A.,  de  Spatulariarum 
Anat.  Inaug.  Diss.  Berol.  '75  WILDER,  B.,  Notes  on  Am.  Gan. 
I.  Respir.  of  Lepid.  and  Amia.  II.  Tail  formation  of  Lepid. 
III.  Pect.  fin  formation  of  Lepid.  IV.  Brains  of  Amia,  Lepid., 
Acip.,  and  Polyod.  P.  Am.  Ass.  Adv.  Sci.  xxiv,  151-193. 
'76  Brains,  Philadel.  Acad.  P.  xxxviii,  51-53.  '78  Amia  and 
Lepid.  rudimentary  spiracle,  P.  Am.  Ass.  (unpub'd),  and  Am.  Nat. 
xix,  192.  And  in  the  respiration  of  Amia,  P.  Am.  Ass.  306- 
313.  '85  WRIGHT,  R.  R.,  Notes  on  anat.  of  fishes:  A.  Cutan- 
sense  organs.  B.  Spiracular  cleft  of  Amia  and  Lepid.  C.  Aud. 
organ  of  Hypophthalmus,  Am.  Nat.  xix,  187-190  and  513.  D. 
Hyomand.  clefts  and  pseudobranchs  of  Amia  and  Lepid.  and 
Amia,  J.  Anat.  Phys.  xix,  477-497.  E.  Amia's  serrated  append- 
ages, Sci.  iv,  511.  '87  ZOGRAFF,  N.,  Monograph  (Russians)  on 
Sturgeon,  Tr.  S.  Nat.  Mosc.  Hi,  pp.  72.  '87  Affinities  of  ganoids, 
Nat.  xxxvii,  70. 

SKELETON. — '77  BRIDGE,  T.,  Cranium  Amia  J.  Anat.  Phys.  xi, 
605-622.  '78  Polyodon,  Phil.  Trans,  clxix,  683-734.  '89 
Cranial  anat.  Polypterus,  P.  Birmingham,  Phil.  S.  vi,  118-130. 
'83  CAFAUEK,  F.  (Prag.).  '47  FRANQUE,  H.,  Amia,  Folio, 
Berolini.  '78  GOETTE,  A.,  Wirbelsaule,  A.  mikr.  Anat.  x,  442- 
641.  '93  HASSE,  C.,  Wirbelsaule,  Z.  Wiss.  Zool.  76-90.  '60 
KOLLIKER,  Ende  d.  Wirbelsaule,  Leip.  '20  KUHL  u.  HASSELT 
Ost.  of  Sturgeon,  Kuhl's  Beitr.  Zool.  in  Vergl.  Anat.  2  Abth. 
188-202.  '51  MOLIN,  R.,  Scheletro  dell.  Acipenser,  SB.  Acad. 
Wien,  vii,  357-378.  '82  PARKER,  W.  K.,  Skull  (and  develop.)  of 
Acip.  P.  Roy.  S.  142-145,  of  Lepidos.  443-491.  '83  SAGEMEHL, 
M.  (Skull  of  Amia),  Morph.  JB.  ix,  177-227.  '92  SCHMIDT,  L. 
(Vertebras  of  Amia),  Z.  wiss.  Zool.  liv,  748-764.  '85  SHUFELDT, 
R.  W.,  Amia,  R.  U.  S.  F.  C.  ('83)  747-834.  '70  TRAQUAIR,  R. 
H.,  Calamoichthys,  J.  Dub.  Geol.  Soc.  June  8.  '70  Skull  of 
Polypterus,  J.  Anat.  Phys.  v,  166-183.  '82  WIJHE,  J.  W.  VAN, 
Visceralskelet  (u.  Nerven)  —  includes  Ceratodus,  —  Nied.  A.  Zool. 
v,  207-320. 


248 


FISHES,   LIVING  AND  FOSSIL 


MUSCLES.  — '85  McMuRRiCH,  J.  P.,  Head  of  Amia,  Stud.  Biol.  Lab. 
J.  Hop.  Univ.  iii,  121-153.  '82  SCHNEIDER,  H.,  Augenmuskeln, 
Jen.  Z.  xv,  215-242. 

INTEGUMENT,  TEETH.  — '78  BARKAS,  W.,  Teeth  of  Lepid.  Tr. 
Roy.  S.  N.  S.  Wales,  xi,  203-207.  '77  MACKINTOSH,  H.  W., 
Scale  of  Amia.  (?).  '80  PAWLOW,  H.,  Teeth  of  Sturgeon,  Arb. 
St.  Petersb.  Nat.  Gesell.  No.  9,  494~5°8-  '59  REISSNER,  Schup- 
pen  v.  Polyp,  and  Lepid.  A.  f.  Anat.  '87  ZOGRAFF,  N.,  Zahne  d, 
Knorp.  gan.  Biol.  Centralb.  vii,  178-183  and  224. 

VISCERA.  — '86  CATTANEO,  G.,  Olandula  gastriche  nell'  Acip.  Rend. 
Inst.  Lomb.  xix,  676-682.  '78  FURBRINGER,  Excretory  sys.  Morph. 
JB.  iv,  56-60.  '72  HERTWIG,  R.,  Lymph.  Driisen  d.  Stbrherzens, 
A.  mikr.  Anat.  ix,  62-79.  HOEVEN,  J.  v.  D.  (Air-bladder  of 
Lepid.)  4to.  (?).  '91  HOPKINS,  G.  S.,  Structure  of  stomach 
of  Amia,  P.  Am.  Micr.  S.  xxii,  165-169.  '92  Diges.  tracts  of 
N.  A.  Gan.  P.  Am.  Ass.  xli,  197.  '69  HYRTL,  J.,  Blutgefasse 
d.  aus.  Kiemendeckel-Kieme  v.  Polyp.  SB.  Ak.  Wien,  Ix,  109-113. 
'86  MACALLUM,  A.  B.,  Diges.  tract  and  pancreas  of  Acip.,  Amia, 
Lepid.  J.  Anat.  Phys.  xx,  604-636.  '91  SEMON,  R.,  Zusammen- 
hang  d.  Harn-  und  Geschlechtsorgane,  Morph.  JB.  xvii,  623-635. 
'77  STOHR  (Valves  in  conus — compares  sharks'),  Morph.  JB.  ii, 
197-228.  '90  VIRCHOW,  H.,  Spritzlochkieme  v.  Acip.  A.  Anat. 
Phys.  (Phys.  Abt.)  586-588.  '86  WILDER,  Serrated  appendages 
of  Amia,  P.  Am.  Ass.  xxxiv,  313-315. 

FINS.  —  '94  GEGENBAUR,  Flossenskelet  d.  Crossopterygier,  Morph. 
JB.  xxi,  119-160.  '82  RAUTENFELD,  E.  V.,  Skel.  hint.  Glied- 
massen,  Inaug.  Diss.  Dorpat,  47  pp.  '77  THACHER,  J.,  Ventral 
fins,  Tr.  Connec.  Acad.  iv,  233-242.  '80  DAVIDOFF,  M.  V., 
Skel.  d.  hint.  Gliedmassen,  Morph.  JB.  vi,  126-128  and  433-468. 
'66  HUXLEY,  Illus.  of  struc.  of  Crossopt.  4to,  Lon. 

NERVOUS  SYSTEM,  END  ORGANS.  — '89  ALLIS,  Lateral  line 
of  Amia,  J.  of  Morph.  '83  CATTIE,  J.  T.,  Epiphysis,  Z.  wiss. 
Zool.  xxxix,  720-722,  and  A.  de  Biol.  iii,  101-196.  '94  COL- 
LINGE,  W.  E.,  Sensory  canals,  of  Polypterus,  P.  Birmingh.  S. 
viii,  255-262  ;  of  Lepid.  op.  cit.  263-272  ;  of  Polyodon  Q.  J.  M.  S. 
xxxvi,  499-437.  '83  DOGIEL,  A.,  Retina,  A.  mikr.  Anat.  xxii,  419- 
472,  and  '84  Naturf.  Ges.  Kasan,  xi,  124  pp.  '86  Geruchsorgan,  Tr. 
Kasan.  Univ.  xvi,  82  pp.  '88  Retina,  Anat.  Anz.  iii,  133-143. 
'79  Gisow,  A.,  Gehb'rorgan,  Bonn.  '81  Gisow,  A.,  Gehororgan, 
A.  mikr.  Anat.  xviii,  484-519.  '88  GORONOWITSCH,  N.,  Gehirn 
u.  Cranialnerven  v.  Acip.  Morph.  JB.  xiii,  427-514.  '70 


BIBLIOGRAPHY:    TELE  OS  TS 


249 


MIKLUCHO-MACLAY,  N.  v.,  Mittelhirn,  Leip.  4to,  pp.  74.  '81 
RETZIUS,  Gehb'rorgan  v.  Polyp.  Stockh.  '81  SCHNEIDER,  H., 
Augenmuskelnerven,  Jen.  Z.  viii,  215-242.  '87  WALDSCHMIDT, 
J.,  Centr.  nerv.  u.  Geruchsorg.  v.  Polyp.  Anat.  Anz.  ii,  308-322. 
DEVELOPMENT.  — '78  AGASSIZ,  A.  (Larva?  of  Lepid.),  P-  Am. 
Acad.  A.  and  Sc.  xiii,  65-76.  '89  ALLIS,  E.  P.,  Lateral  line, 
Amia,  J.  of  Morph.  '81  BALFOUR  and  PARKER,  Str.  and  devel.  of 
Lepid.  P.  Roy.  S.  xxiii,  112-119,  and  '82  in  Phil.  Trans,  (large 
memoir).  '89  BEARD,  J.,  Early  devel.  of  Lepid..  P.  R.  S.  xlvi, 
108-118.  '95  DEAN,  B.,  Early  devel.  gar  and  sturgeon,  J. 
Morph.  xi,  No.  I,  1-62.  '82  DUNBAR,  G.,  Breeding  of  Lepid. 
Am.  Nat.  May.  '94  FULLEBORN,  F.  (Breed,  habits  Amia  and 
Leipd.),  SB.  Akad.  Wiss.  Berl.  xl,  1-14.  '67  GEGENBAUR,  Wir- 
belsaule  d.  Lepid.  Jen.  Z.  iii,  359-414.  '93  JUNGERSEN,  H.  F.  E., 
Embryonalniere  d.  Stors,  Zool.  Anz.  464,  and  ('94),  Amia,  op.  cit. 

No.   451.      '70   KOWALEWSKY,   OWSJANNIKOW,   U.  WAGNER,    Stor, 

B.  Acad.  St.  Petersb.  xiv,  287-325,  and  Mel.  Biol.  du  B.  Acad. 
St.  Petersb.  vii,  171-183.  '91  KUPFFER,  K.  v.,  Kopf.  v.  Acip. 
SB.  Gesell.  Morph.  Miinchen,  107-123,  and  ('93)  memoir,  Leh- 
man. Munchen.  '90  MARK,  E.  L.,  B.  Mus.  Comp.  Zool.  xix, 
1-127.  '82  PARKER,  W.  K.,  Skull  of  Lepid.  and  Acip.  P.  Roy. 
S.  '87  PELTSAM,  E.  D.,  Segmentation  (Russian),  MT.  Gesell. 
Mosc.  Univ.  I,  Heft  i,  and  Protocolle  d.  SB.  Zool.  Sect. 
Mosc.  ('86)  I,  Heft  i,  206.  '89  RYDER,  J.  A.,  Sturgeon,  Am. 
Nat.  xxii,  659-660,  and  ('90)  B.  U.  S.  F.  C.  viii,  231-281.  '78 
SALENSKY,  W.,  Sturgeon,  SB.  Gesell.  Nat.  Kasan  ('77),  34 
(Russian).  Also  Post-Emb.  Entvvickel  op.  cit.  ('78)  21  (Rus- 
sian). (Segmentation)  Zool.  Anz.  ('78)  243-245,  and  (Skeleton) 
266-269,  288-291.  (General)  Mem.  S.  Nat.  Univ.  Kasan,  vii 
1-226  (Russian).  '80  Pt.  II,  Post-Emb.  and  Organogeny,  op. 
cit.  x,  227-545.  Abstract  in  HOFMAN  and  SCHWALBE'S  JB.  vii. 
213,  217-225.  '81  (French),  A.  de  Biol.  ii,  233-278. 

THE   TELEOSTS 

(Literature  greatly  summarized.) 

GENERAL  ANATOMY.  — '93    PARKER,   T.    J.,   Zootomy   (Cod). 

'88  ROLLESTON,  Forms  of  animal  life,  83-102,  and  '95  VOGT  and 

JUNG,  Anatomic   comparee,  Vol.  II.     '80   EMERY,  C.,  Fierasfer, 

Fauna  u.  Flora  d.  Golfes  v.  Neapel,  ii. 
SKELETON.  — '83  BROOKS,  H.  S.,  Haddock,  P.  Roy.  S.  Dub.  iv, 

166-196.     '90  GILL,  T.,  Skeleton,  notes,  P.  U.  S.  Nat.  Mus.  xiii, 


250 


FISHES,   LIVING  AND  FOSSIL 


157-170,  231-242,  377-380.  '79  GOETTE,  A.,  Wirbelsaule  u. 
Anhange,  A.  mikr.  Anat.  xvi,  117-142.  '84  GOLDI,  E.  A.  (Derm 
bones  of  Catfish,  Balistes,  Acipenser),  Jen.  Z.  xvii,  401-447.  '82 
KOSTLER,  M.,  Knochenverdickungen,  Z.  wiss.  Zool.  xxxvii,  429- 
456.  '73  VROLIK,  A.,  Verknbckerang,  Nied.  Arch.  Zool.  219-314. 

TEETH,  INTEGUMENT.— '78  BOAS,  J.  E.  V.  (Scarid  dentition),  Z. 
wiss.  Zool.  xxxii,  189-215.  '78  CARLET,  M.,  Ecailles,  Ann.  Sci. 
Naturelle,  viii,  Art.  8.  '86  SCHAFF,  E.,  Lophobranchier,  Inaug. 
Diss.  Kiel. 

VISCERA,  GLANDS,  CIRCULATORY.  — '80  BOAS,  J.  E.  V., 
Conus,  Morph.  JB.  vi,  527-533.  '87  BROCK,  J.,  Urogenital,  Z. 
wiss.  Zool.  xlv,  532-541.  '91  CALDERWOOD,  W.  L.,  Head  kidney, 
J.  Mar.  Biol.  Ass.  ii,  43-46.  '82  EMERY,  C.  (Kidney),  A.  Ital. 
Biol.  ii,  135-144,  Atti.  Ace.  Rom.  xiii,  43-49,  ('85)  Zool.  Anz. 
viii,  742-744.  '77  FURBRINGER  (Excretory),  Morph.  JB.  iv,  43- 
49.  '83  MAURER,  F.,  Pseudobranchien,  op.  cit.  ix,  229-251.  '86 
Thymus,  op.  cit.  xi,  129-172.  '86  WEBER,  M.,  Abdominalporen 
(Geschlechtsorgane),  op.  cit.  xii,  366-406. 

SWIM-BLADDER.  — '90  BRIDGE,  T.  W.,  P.  Birm.  Phil.  S.  vii,  144- 
187.  '89  BRIDGE  and  HADDON,  A.  C.,  Siluroids,  P.  Roy.  S.  xlvi, 
309-328,  Phil.  Trans.  ('93)  clxxxiv,  65-333.  '88  CORNING, 
H.  K.,  Wundernetz,  Morph.  JB.  xiv,  1-53. 

NERVOUS -SYSTEM,  END  ORGANS.— '82  CATTIE,  J.  T.,  Epiph- 
ysis,  A.  Biol.  iii,  101-196.  '88  CHEVREL,  R.,  Sympathetic, 
C.  R.  cvii,  530-531.  '91  GUITEL,  F.,  Ligne  latdrale,  A.  Zool. 
expe'r.  ix,  125-190,  671-697.  '92  HERRICK,  C.  L.,  Fore-brain, 
Am.  Nat.  xxvi,  112-120,  and  Anat.  Anz.  vii,  422-431.  '87  LEN- 
DENFELD,  R.  v.,  Phosphorescent  organs,  Challenger,  xxii,  277- 
329.  '81  MAYSER,  P.,  Gehirn,  Z.  wiss.  Zool.  xxxvi,  259-364.  '84 
S^DE  DE  LIEOUX,  P.  DE,  Ligne  laterale.  Paris,  115  pp. 

EMBRYOLOGY,  GENERAL.  — '91  WILSON,  H.  V.,  Sea-bass, 
U.  S.  F.  C.  B.  ix,  209-277  (with  references).  '81-'91  RYDER,  J. 
A.,  U.  S.  F.  C.  R.  and  B.  Larval  Teleosts:  '77  AGASSIZ,  A.,  P.  Am. 
Acad.  v,  117-126,  ('78)  xiv,  pp.  25,  ('82)  271-303,  and  Mem. 
Mus.  Comp.  Zool.  xiv,  1-56.  '87  CUNNINGHAM,  J.  T.,  Tr.  Roy.  S. 
Edinb.  xxxiii,  97-136,  ('91)  J.  Mar.  Biol.  Ass.  ii.  '83  HILGEN- 
DORF,  SB.  Nat.  Fr.  43-45.  '90  HOLT,  E.  W.  L.,  Sci.  Tr.  R.  Dub. 
S.  432-474-  '80  LUTKEN,  C.,  Dan.  Selsk.  xii,  413-613.  '91 
MclNTOSH,  W.  C.,  R.  Fish.  Scot,  ix,'  317-342.  '90  MC!NTOSH  and 
PRINCE,  Edinburgh,  4to.  '87  RAFFAELE,  F.,  MT.  z.  Stat.  Neap. 
viii,  1-84,  ('90)  ix,  305-329. 


BIBLIOGRAPHY:    TELEOSTS  25 1 

HERMAPHRODITISM.  — '91  HOWES,  G.  B.,  J.  Linn.  S.  xxiii,  539- 
558.  '67  JACKEL,  H.,  AH.  Nat.  Gesell.  Num.  iii,  245.  '76  MALM, 
A.  W.,  CE.  v.  Ak.  Forh.  Stockholm.  '67  SMITH,  J.  A.,  P.  Roy.  S. 
Edinb.  '64  '65,  300-302,  ('70)  J.  Anat.  Phys.  iv,  256-258.  '91 
SMITH,  W.  R.,  R.  Fish.  Scot,  ix,  352.  '84  WEBER,  M.,  Ned. 
Tijdschr.  Amst.  21-43,  C87)  128-134. 

VIVIPAROUS  DEVELOPMENT.  — '85  RYDER,  P.  U.  S.  Nat.  Mus. 
viii,  128-156  (with  references) . 


FISHES,  LIVING  AND  FOSSIL 


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Figs.  310-315.  —  Skulls  of  fishes,  to  illustrate  the  mode  of  articulation  of  jaws  and 
branchial  arches.  310.  Skull  of  Scyllium.  (After  MARSHALL  and  HURST.)  311.  Hep- 
tanchus  (Notidanus).  (After  HUXLEY.)  312.  Chim&ra.  9  313.  Ceratodus.  (Slightly  modi- 
fied after  HUXLEY.)  314.  Polypterus.  315.  Salmon.  (After  PARKER.) 

A.  Articular.  AG.  Angular.  BR.  Branchiostegal  rays.  CHY.  Ceratohyal.  D. 
Dentary.  EHY.  Epihyal.  EPH,  LG.  Epihyal  ligament.  EPO.  Epiotic.  F.  Frontal. 
GHY.  Glossohyal.  HHY.  Hypohyal.  HM.  Hyomandibular.  IO.  Interoperculum. 
J.  Jugal.  LC.  Labial  cartilages.  MCK.  Meckel's  cartilage.  MPT.  Metapterygoid. 
MSPT.  Mesopterygoid.  MX.  Maxillary.  N.  Nasal.  NC.  Nasal  capsule.  O.  Opercu- 
lum.  OC.  Opercular  cartilage.  OR.  Suborbital  ring.  P.  Parietal.  PAL.  Palatine. 
PMX.  Premaxillary.  PO.  Preoperculum.  PTO.  Pterotic.  PTQ.  Palatoquadrate. 
PTY.  Palatopterygoid.  Q.  Quadrate.  SQC.  Supraoccipital.  SE.  Supra-ethmoid.  SM. 
Symplectic.  SO.  Supraorbital.  SP.  Splenial.  UMC.  Upper  median  cartilage  (not 
frontal  spine  of  male). 

Figs.  310,  314,  315  are  regarded  by  HUXLEY  as  "hyostylic"  (i.e.  the  hyoid  element, 
HM,  attached  by  ligaments  to  the  jaw  hinge,  taking  an  important  part  in  the  suspension 
of  the  jaw;  311,  a  modified  hyostylic  condition  ;  the  hinder  upper  margin  of  PTQ  becom- 
ing greatly  enlarged,  and  attached  by  ligaments  to  the  skull,  is  spoken  of  as  "amphistylic  "  ; 
312-313,  were  "  autostylic,"  i.e.  the  upper  jaw  element  fused  with  the  skull. 

254 


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Figs.  316-325.  —  Heart  and  arterial  cone  of  fishes.  316.  Heart  of  shark;  317,  Heart 
of  catfish,  Silurus  glanis  ;  318,  Heart  of  shark,  shown  opened  at  the  side.  319.  Conus 
arteriosus  (inner  view)  of  Chimcera,  320.  Conus  of  Ceratodus.  321.  Conus  of  Protopte- 
rus.  322.  Conus  of  Lepidosteus.  323.  Conus  of  Amia.  324.  Conus  and  bulbus  of  the 
Teleost,  Butrinus,  325.  Conus  and  bulbus  of  the  Teleost,  Clupea.  (Figs.  316-318 
after  WIEDERSHEIM,  320-325  after  BOAS.) 

A.  Aorta.    AU.  Auricle.    B.  Bulbus.     C.  Conus.     V.  Valves.     VEN.  Ventricle. 

258 


Pigs.  9-12.  —Arrangement  of  gills  of  Bdellostoma  (9),  Myxine  (10),  Shark  (n),  and 
Teleost  (12).  In  each  figure  the  surface  of  the  head  region  is  shown  at  the  left. 

B.  Barbels.  BD.  Outer  duct  from  gill  chamber,  BS.  BO.  Common  opening  of  outer 
ducts  from  gill  chambers.  BS.  Branchial  sac,  or  gill  chamber.  BS".  Branchial  sac,  sec- 
tioned so  as  to  show  the  folds  of  its  lining  membrane.  G.  Lining  membrane  of  gullet. 
GB.  Gill  bar,  supporting  vessels  and  filaments  of  gills.  GC.  Outer  opening  of  gill  cleft. 
GF.  Gill  filament.  GR.  Gill  rakers.  GV.  Vessels  of  gill.  JtJ'.  Upper  and  lower  jaw. 
M.  Mouth  opening.  N,N'.  Anterior  and  posterior  opening  of  nasal  chamber.  OP.  Oper- 
culum.  SP.  Spiracle.  ST.  Tendinous  septum  between  anterior  and  posterior  gill  filaments. 
*  Denotes  the  inner  branchial  opening;  -»,  the  direction  of  the  water  current. 

259 


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FIG.  326 


Figs.  326-331.  — Digestive  tracts  of  fishes.  326.  Cyclostome,  Petromyzon.  327.  Shark. 
328.  Chimaeroid,  Callorhynchus.  329.  Lung-fish,  Protopterus.  (After  W.  N.  PARKER.) 
330.  Ganoid,  Acipenser  sturio.  331.  Perch.  (After  WlEDERSHElM.) 

A.  Anus.  BC.  Branchial  chamber.  BE.  Bursa  entiana  (duodenum) .  CL.  Cloaca. 
GC.  Gill  openings.  7.  Intestine.  M.  Mouth.  MI.  Mid-gut.  NN'.  Anterior  and  poste- 
rior nares.  OE.  Gullet.  PC.  Pyloric  coeca  (pancreas).  PY.  Pyloric  end  of  stomach. 
R.  Rectum.  RG.  Rectal  gland.  S.  Stomach.  SP.  Spiracle.  SP.  V.  Spiral  intestinal 
valve. 

262 


DIGESTIVE   TRACT 


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LI  caecum;  cloaca.  Mesentery  at  beginning  and  end  of  digestive 
ierced  with  5  (6  or  7)  gill  clefts  ;  spiracle  present,  its  gill  supplied  bj 
ent  in  Chlamydoselache. 

almost  straight,  no  marked  stomachic  dilation;  injestine  with  sp 
•y  reduced  to  4  string-like  supports.  No  spiracle  ;  gill  arches  5,  com] 
,  with  rudimentary  cartilaginous  supports. 

>w  gullet,  tubular  stomach,  intestine  with  spiral  valve  of  9  turns, 
y  greatly  reduced.  No  spiracle  ;  5  gill  arches  ;  hyoidean  gill. 

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5  gill  arches,  of  which  the  hinder  3  present  external  branchiae. 

t  ;  a  single  pyloric  caecum,  spiral  valve  of  8  turns,  no  cloaca,  single  (or 
odont. 

stomach,  recurved  at  end;  a  mass  of  pyloric  caeca;  short,  twisted,  s 

Ive  of  3  (rudimentary)  turns.  No  cloaca.  Well-marked  dorsal  mese 
ial  stomach  ;  pyloric  caeca  in  fused  mass  (but  separate  in  Polyodon)  ; 
Ive  of  8-9  turns  ;  no  cloaca.  Dorsal  mesentery  largely  fenestrated. 

pouch-like  stomach,  no  pyloric  caeca;  long,  stout,  small  intestine,  littl 
Ive  of  4  turns  ;  no  cloaca.  Dorsal  mesentery  at  hind  gut  largely  fene 

ct  of  many  types  ;  stomach  usually  recurved  ;  many  pyloric  caeca  ;  in 
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Figs.  13-19.  —  Air-bladder  of  fishes,  shown  from  the  front  and  sides.  Cf.  p. 
264.  A.  Air-  or  swim-bladder.  AD.  Air  duct.  D.  Digestive  tube.  (After  WILDER.) 
13.  Sturgeon  and  many  Teleosts.  14.  Amia  and  Lepidosteus.  15.  Erythrinus,  a 
Cyprinoid  Teleost.  16.  Ceratodus.  17.  Polypterus  and  Calamoichthys.  18.  Lepi- 
dosiren  and  Protopterus.  19.  Reptiles,  birds,  and  mammals.  The  diagrams  illus- 
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Figs.  332-337.  —  Urinogenital  ducts  and  their  external  openings.  332.  Cyclostome, 
Pctromyzon.  (After  W.  K.  PARKER.)  333.  Shark,  ?.  334.  Chimaeroid,  juv.  9.  335. 
Cerahdus.  336.  Ganoid,  $.  337-  Teleost  (Salmonoid),  ?.  (After  BOAS.) 

A.  Anus.  AP.  Abdominal  pore.  CL.  Cloaca.  G.  Genital  opening.  MD,  MD' . 
Left  and  right  Miillerian  ducts.  OVD,  OVD'.  Left  and  right  oviducts  (not  Miillerian 
ducts).  R.  Rectum.  U,  U' .  Left  and  right  ureters.  UG.  Urinogenital  opening.  UG' ', 
UG".  Left  and  right  Urinogenital  ducts.  UGP.  Urinogenital  papilla,  showing  distal 
opening.  UGS.  Urinogenital  sinus.  UP.  Urinary  papilla. 

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-  339-344'  —  The  brain  of  fishes.  The  dorsal  view  of  each  brain  is  shown  in  the 
upper  figure,  the  ventral  view  immediately  below.  339.  Bdellostoma.  (After  JOH. 
MiJLLER.)  340.  Petromyzon  (Ammoccetes  stage).  (After  ZlEGLER'S  model.)  341. 
Shark  (angel-fish,  Squatind).  (After  DUMERIL.)  342.  Chimczra.  (After  WILDER.) 
343.  Lung-fish,  Protopterus.  (After  BURCKHARDT.)  344.  Perch,  Perca.  (After  T.  J. 
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272 


342 


Epiphysis.  EP.  Epencephalon.  IN.  Infundibulum.  LH.  Lobus  hippocampi.  LI.  Lobi 
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metencephalon.  P.  Prosencephalon  (cerebral  hemispheres).  P T.  Pituitary  body.  R. 
Olfactory  lobes.  SV.  Saccus  vasculosus.  T.  Thalamencephalon.  ¥4.  Fourth  ven- 
tricle. Numbers  I-X.  Cranial  nerves,  i.  First  spinal  nerve. 
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232  FISHES,  LIVING  AND  FOSSIL 

XIX.    THE   SUPPOSED    DESCENT 

Interrelationships   and   lines    of  descent   as   suggested   by  a  number  of 
noted  on  each  scheme.     *  Denotes  that  the  diagram  is  the  present  writer's 


Howes  ('91)  * 

(On  TJrino  Genital  System) 


Smith  Woodward  ('92)' 
(On  Palaeontology) 


Nephrorchidic 

(Elasmobranchs 

Batraehians 

Amniotes) 


L    A 


thorchidic 

(Ganoids 

Teleosts 

Marsipobranchs 

Dipnoans) 


Haeckel('93)* 

(On  General  Anatomy) 


Ci ossopterygiana 


Rays 


Cycles  tome 


Selachian 


Palaedipneusten 

Proganoid          \ 

.  Dipnoau    ' 

\  \ 

Ganoid  and  \ 

Teleost          Amphibian 


lUy 


Klaatsoh  ('93) 

(On  Axial  Skeleton) 


Cartilaginous 
Chordal  Verte- 
brae 


Perichordal  Cartilaginous 
Vertebrae 


W.N.  Parker  ('92)* 
(On  General  Anatomy) 


Shark  Acipenser  \      Teleost 

Lepidosteus 
Cope  ('85)* 
(On  General  Anatomy  and  Palaeontology) 


Chimaeroid 


Ichthyotome 


Burekhardt  ('92) 
(On  Central  Nervous  System) 
Selachian  /     v Petromyzon 


7 


Retziua  ('98) 

(Nervous  System  and  End  Organs) 


Ceratodus 


Dipnoan 

\ 


Protopterua 


Reptile 


Myxine 


Proganoid  A 
Acipenser 


Amphibia 


Teleosts 


Bony  Ganoids 


•  Petromyzon 


SUPPOSED  DESCENT   OF  GROUPS 


283 


OF   THE   GROUPS    OF   FISHES 

observers  ;   their  views  have  been  based  on  the  different  lines  of  investigation 
interpretation  of  the  text  of  the  author  cited. 


Balfour  ('80) 
(On  Embryology  and  Anatomy) 

Giinther  ('80)* 

\"      V 

rcnlatory  System)              includes  Lancelet  and  Cyclostomes 
/                                           as  2  Sub  classes  of  Fishes 

/    V                                       Palaekhthys 

/ 

ay  Ganc 

ids            N.                                                    \              \ 

. 

\\                                              Ganoids 
\Amphibia                 ^-^  DipIJOans) 
Protopterus 
Chondrosteans 
ratodus                                           (Sharks  and  Chimaeroids) 

leiewu 

Gill  ('95) 

(On  Structural  Characters) 

//j\\                                                                   »avldoff('80) 

/  1  \  \\vV           —  Pleuracanthid                         (On  Extremities  and  Girdles) 

,,     .     /  /  /        \\V                                                                Primitive  Gnathostome 
Wynne7    /    |         \  \\Teleostome                                                            | 

Petromyion'    J            \  \Dipnoan 

I                                             1 

Chimaeroid            Elasmobranch 

Scaphyrhynchus 

|                                   Selachian 

Bridge  C?8) 

JVcipcnccr 

(On  Osteology  of  Ganoids) 

I                          Shark               Rays(!) 

1 

Polyodon                        |        "Chimaeroid 

Apneumato-—  | 
coela                                                     —  Pneuma 
|                                                   coela 

Heptanchus        Acanthias 

1 

Polypterus 

.hlasmobrancn 

Amia                          Lepidosteus 
1                                       | 

~1 

1                  Amphib 

ia                      ,     o 

Selachoidei 

Teleosteoidei 

(On  Embrj'olog}-)   ' 

c 

^X—  . 

(On  Anatomy  of  Head) 

Beard  ('90) 

\Shark 

(On  Embryology  and  Brain) 

Selachians                          Crossopterj-gian 

/ 

Ctenodipterini         N. 

Selachodichthyidae 

Ganoids                                   (Devon)                  N^^ 

I                                  Tel 

/\                                    ^hlb" 

eosts         \AmpTiibia                   Ceratodus 

andProtamnia              /  (Trias) 

^r          ^W 

~~*7               1      '\. 

/                N. 

Ischyodus/            /       Ceratodus 

/                         ^v 

(Jura)/              / 

Selachians                         >v 

/     pL 

>.                               Holocephali 
Dipnoans  and 

Amphibia 

INDEX 


Abdominal  pores,  271. 

Acanthias,  larva  of,  21 6  (Figs.  288, 
289). 

Acanthodes,  gill  shields,  20;  a  fossil 
shark  of  the  Coal  Measures,  79; 
structure  of,  80,  8i;  A.  wardii,  81 
(Fig.  87) ;  shagreen  and  denticle  of 
A.  gracilis,  8 1  (Fig.  88);  affinities 
of,  95;  diagram  of  affinities,  98 
(Fig.  103) ;  gill  arches,  1 14. 

Acanthodians,  antiquity  of,  9;  fin 
spine  and  pectoral  fin,  28,  29  (Fig. 
32);  pectoral  fin  of  Parexus,  42 
(Fig.  51),  44. 

Acanthodopsis  wardii,  teeth  of,  82 
(Fig.  88  A}. 

Acanthopterygian,  166  (Fig.  171  A). 

ACANTHOPTERYGII,  in  classification,  9 ; 
as  a  subdivision  of  Teleocephali,  174. 

Acipenser,  in  classification,  8;  antiquity 
of,  9,  1 66  (Fig.  171  A};  swim-blad- 
der of,  22  (Fig.  1 3) ;  description  of, 
159-161;  A.  sturio,  160  (Fig.  165); 
eggs  and  breeding  habits,  181  (Fig. 
194),  185;  fertilization,  187;  devel- 
opment of  eggs,  203  (Figs.  249- 
264),  207;  larval  development  of, 
221-223  (Figs.  296-302);  heart, 
oonus  and  bulbus  arteriosus,  tables, 
260;  gills,  spiracle,  gill  rakers  and 
opercula,  tables,  261 ;  digestive  tract, 
tables,  262  (Figs.  326-331);  swim- 
bladder,  tables,  264,  265  (Fig.  13); 
genital  system,  tables,  266;  urino- 
genital  ducts  and  external  openings, 
tables,  267  (Figs.  332-337) ;  excre- 
tory system  and  urinogenital  ducts, 
tables,  271. 


ACTINOPTERYGII,  in  classification,  8, 
147;  description  of,  155-178  (Figs. 
157-185  A)\  Chondrosteans  (Gan- 
oids), 155;  fossil  forms,  155-159 
(Figs.  158-164);  living  types,  159- 
178  (Figs.  165-185  A}. 

Actinotrichia,  31,  33  (Fig.  39). 

dZtheolepis,  ganoid  plates  of,  24  (Fig. 

25),  25. 

Agassiz,  L.,  37,  66,  107,  ill. 
Agassiz,  A.,  224. 
Air-bladder,  v.  Swim-bladder. 
Allis,  E.  P.,  50,  51. 
Alopias,%<);  A.vulpes  (thrasher shark), 

89  (Fig.  95). 
Alosa,  eggs  and  breeding  habits,  181 

(Fig.  I97)>  186. 

American  Arthrodirans,  130. 

American  Geologist,  80. 

Amia,  in  classification,  8;  antiquity 
of,  9,  1 66  (Fig.  171  A);  swim-blad- 
der of,  21,  22  (Fig.  14) ;  sensory 
tracts  in  head  dermal  plates,  and 
scales  of,  50-52  (Figs.  64-68) ;  A. 
calva,  51  note;  a  Ganoid  with  her- 
ring-like scales,  145 ;  description  of, 
163-165  (Figs.  167,  168);  Mesozoic 
forms,  164,  165  (Figs.  169-171); 
heart,  conus  and  bulbus  arteriosus, 
tables,  260;  gills,  spiracle,  gill  rakers, 
and  opercula,  tables,  261 ;  digestive 
tract,  tables,  263;  swim-bladder, 
tables,  264,  265  (Fig.  14);  genital 
system,  tables,  266;  excretory  sys- 
tem and  urinogenital  ducts,  tables, 
271. 

Amiurus,  barbels  of,  46,  47  (Fig.  58). 

Ammoccetes,  head  of,  61  (Fig.  72  C"), 


285 


286 


INDEX 


62;   development  of  egg,  189  (Fig. 

215)- 
Amphibian  affinities  of  the  shark,  98 

(Fig.  103). 
AMPHIOXUS,  in  classification,  7;   gills 

of,  1 6. 

ANACANTHINI,  174. 
Anal  fins,  v.  Fins. 
Anatomy,  v.  Shark,  Cladoselache,  Acan- 

thodes,     Climatius,    Pleuracanthus, 

Chondrenchelys,  Chimcera,  Dipnoan, 

etc. 

Angel-fish,  v.  Rhina. 
Anguilla,  v.  Eel. 
APODES,  173. 

Aquatic  breathing,  1 6-23 ;  modes  of,  20. 
Archipterygium,  39. 
Arius,  eggs  and  breeding  habits,  181 

(Fig.  195),  i85»  l86- 

Armour  plates,  23;   evolution  of,  25. 

ARTHRODIRA,  in  classification,  8;  de- 
scribed, 129-138  (Figs.  130-144); 
geological  position  of,  9,  129;  asso- 
ciated with  Pterichthys  by  Traquair, 
130;  American,  described  by  New- 
berry  and  by  Claypole,  130;  Din- 
ichthys,  130  (Frontispiece  and  Figs. 
I33~137)  ;  varying  size  of,  136;  den- 
tition, jaws,  and  mandibles,  136,  137 
(Figs.  138-144)  ;  affinities,  136-138; 
differing  from  lung-fishes  and  from 
sharks,  136  note. 

Aspidorhynchiis,  157;  A.  acutirostris, 
158  (Fig.  162). 

Aspredo,  eggs  and  breeding  habits,  186. 

Authors,  comparison  of  phylogenetic 
tables  of,  282,  283;  v.  Bibliogra- 
phy. 

Ayers,  H.,  57,  60,  181. 

Balfour,  F.  M.,  40,  193,  216;  phylo- 
genetic table  of,  compared,  283. 

Barbels,  46-48  (Figs.  55-60). 

Basking  shark,  v.  Cetorhinus. 

Bass,  striped,  numerical  lines  of,  5 
(Fig.  8). 

Bathyonus  compressus,  1 68  (Fig.  172). 

Batrachus,  eggs  of,  1 86. 


Bdellostoma,  gills  of,  17  (Fig.  9); 
anatomy  and  general  description  of 
B.dombeyi,  57,  58  (Fig.  69  A},  59, 
60  (Fig.  70),  61  (Fig.  72  A}\  eggs 
of,  1 80,  181  (Fig.  1 86);  genital  sys- 
tem, tables,  266;  excretory  system 
and  urinogenital  ducts,  tables,  270; 
brain  of,  tables,  272  (Fig.  339) ;  cen- 
tral nervous  system,  tables,  274. 

Bean,  T.  H.,  103,  108,  no. 

Beard,  J.,  57,  61,  146,  217;  phylo- 
genetic table  of,  compared,  283. 

Berycids,  antiquity  of,  9. 

Bibliography,  231-251. 

Blenniids,  eggs  of,  185  (Figs.  198- 
199),  186. 

Blenny,  v.  Blenniids. 

Blood-vessels,  v.  Fishes,  circulation  in, 
Heart,  Chimaeioids,  etc. 

Boas,  J.  E.  V.,  phylogenetic  table  of, 
compared,  283. 

Bohm,  A.  A.,  187. 

Bolau,  H.,  185. 

Bony  fishes,  v.  Teleosts. 

Bow-fin,  v.  Amia  calva. 

Brain,  of  Chimaeroids  and  sharks,  114; 
resemblances  between  lung-fishes 
and  Elasmobranchs,  128;  compari- 
son tables  of,  272  (Figs.  339-341), 
273  (Figs.  342-344),  274-275. 

Branchial  arches,  table  of  relations  of, 
254  (Figs.  310-315).  256-257. 

Breathing,  aquatic,  16—23. 

Breeding  habits,  180-186;  table  of  the 
early  development  of  fishes,  280-281. 

Brevoortia  (menhaden),  gills  of,  20. 

Bridge,  T.,  phylogenetic  tables  of, 
compared,  283. 

Bulbus  arteriosus,  comparative  tables 
of,  258  (Figs.  316-325),  260. 

Bull-head,  v.  Catfish. 

Burkhardt,  R.,  128;  phylogenetic 
table  of,  compared,  282. 

Butrinus,  heart,  conus  and  bulbus  ar- 
teriosus, 258  (Fig.  323) ;  compari- 
son tables  of,  260. 

Calamoichthys,    swim-bladder    of,    22 


INDEX 


287 


(Fig.  17);  median  fins  of,  31;   an- 1 
tiquity    of,    148;     described,    150; 
C.  calabaricus,  147,  150  (Fig.  150). 

Calberla,  E.,  187. 

Caldwell,  W.  H.,  125. 

Callichthys,  respiration  of,  20;  ganoid 
plates. of,  24  (Fig.  26),  26;  origin 
of  dermal  cusps,  30;  C.  armaius, 
172  (Fig.  178);  eggs  and  breeding 
habits,  1 86. 

Callorhynchus,  lateral  line  lost,  49; 
description  of,  104,  109;  mandibu- 
lar,  106  (Fig.  no);  bottle-nosed 
Chimsera,  109  (Fig.  1 1 8);  eggs 
and  breeding  habits  of,  181  (Fig. 
191),  185. 

Canals,  v.  Lateral  line. 

Carassius  aurattis,  170  (Fig.  176). 

Carp,  scales  of,  26  (Fig.  31  A};  eggs 
of,  187. 

Catfish,  barbels  of,  46,  47  (Fig.  58) ; 
description  of,  171,  172;  Amiurus 
me/as,  171  (Fig.  177). 

Cattie,  J.  T.,  54. 

Caturus,  164-165;  C.  furcatus,  164 
(Fig.  169)  ;  Mesozoic  caturid,  166 
(Fig.  171.4). 

Caudal  fins,  35;  evolution  of,  35-39 
(Figs.  44-48). 

Central  nervous  system,  v.  Nervous 
system. 

Cephalaspis,  antiquity  of,  9;  described, 
67;  C.lyetti,  66  (Figs.  78,  79). 

Cephaloptera,  v.  Dicerobatis. 

Ceratodus,  antiquity  of,  9,  10;  swim- 
bladder  of,  22  (Fig.  1 6);  archip- 
terygial  pectoral  fin  of,  39,  40,  42 
(Fig.  54),  44,  45;  description  of, 
123  (Fig.  127),  124;  skeleton  of, 
123  (Fig.  128);  skull  of,  124  (Fig. 
128^4);  embryonic  stages,  125; 
eggs  and  breeding  habits,  181  (Fig. 
192),  185;  development  of  egg, 
198-202  (Figs.  231-248);  larva  of, 
218-221  (Figs.  290-295);  skeleton 
of,  tables,  253;  jaws  and  branchial 
arches,  tables,  254  (Fig.  313),  257; 
.heart,  conus  and  bulbus  arteriosus, 


tables,  258  (Fig.  320) ;  comparison 
tables  of  heart,  etc.,  260;  gills, 
spiracle,  gill  rakers,  and  opercula, 
tables,  261;  digestive  tract,  tables, 
263;  swim-bladder,  tables,  264,  265 
(Fig.  16);  genital  system,  tables, 
266;  urinogenital  ducts  and  external 
openings,  tables,  267  (Fig.  335); 
excretory  system  and  urinogenital 
ducts,  tables,  270;  abdominal  pores, 
tables,  271. 

Cestracion,  antiquity  of,  10;  jaw  of, 
24  (Fig.  27);  caudal  fin,  36,  37 
(Fig.  45),  38;  anatomy  of,  85  (Fig. 
91),  86;  Port  Jackson  shark,  181 
(Fig.  190),  183. 

Cestraciont,  antiquity  of,  9,  10;  gills 
of,  1 6  note;  anatomy  of,  85,  86; 
dentition  of,  86;  affinities  of,  95, 
96;  dental  evolution,  112. 

Cetacean,  fish-like  form  of,  5  (Fig. 
7),  6. 

Cetorhinus,  90  (Fig.  96  A). 

Challenger  report,  quoted,  87,  103. 

Characteristic  structure  of  fishes,  14. 

Cheirodus,  157;  C.  granulosus,  157 
(Fig.  1 60). 

Cheiropterygium,  39. 

Chilomycterus  geometricus,  175,  176 
(Fig.  184). 

Chimcera,  sensory  canals  of  the  head, 
30;  lateral  line  of,  49,  51  note; 
affinities  to  shark,  98  (Fig.  103); 
anatomy  of,  99-101  (Fig.  104); 
skeleton  of,  101-103;  skeleton  of 
C.  monstrosa,  102 (Fig.  105)  ;  genus, 
104;  mandibular,  106  (Fig.  109); 
palatine  plate,  106  (Fig.  109  A); 
clasping  spine  of  forehead,  107  (Fig. 
113);  ventral  fin  and  clasping  organ, 
107  (Figs.  1 1 6,  117);  bottle-nosed 
Chimaera,  109  (Fig.  118);  general 
description,  no  (Fig.  119),  in 
(Fig.  120);  dermal  plates,  113  (Fig. 
104) ;  comparison  tables  of  skeleton 
of,  253;  jaws  and  branchial  arches, 
tables,  254  (Fig.  312),  256;  urino- 
genital ducts  and  external  openings, 


288 


INDEX 


tables,  267  (Figs.  332-33?)  5  ab' 
dominal  pores,  tables,  271;  brain 
of,  273  (Fig.  342). 

CHIM^ROIDS,  in  classification,  7,  8; 
antiquity  of,  9,  10;  gill  shields,  20; 
affinities  to  shark,  96;  general  de- 
scription of,  99-115  (Figs.  104- 
120);  anatomy  of,  99-101  (Fig. 
104);  skeleton  of,  101-103  (Fig. 
105);  embryology  and  larval  his- 
tory of,  103;  fossil  Chimseroids, 
103,  104  (Fig.  105^);  living  Chi- 
mseroids, description  of,  104-111 
(Figs.  117-120);  spines  and  clasp- 
ing organs,  107  (Figs.  113-116); 
affinities,  111-115;  dental  plates, 
in  (Fig.  in);  history  of  fossil 
forms,  112;  dental  evolution,  112; 
structural  affinities  to  shark,  112- 
115;  divergences  from  elasmo- 
branchian  structure,  113;  skull  and 
mandible  of,  1 13;  fins  and  fin  spines, 
113;  skin  defences  and  teeth,  113; 
gill  arches,  114;  brain  of,  114;  lat- 
eral line,  114;  clasping  spine,  114; 
descent  of,  115;  diphycercal  tail 
compared  with  that  of  sharks,  115; 
separated  from  Arthrodirans,  136; 
eggs  and  breeding  habits,  181  (Fig. 
191),  184,  185;  list  of  authors  and 
works  on  the  Chimaeroids,  244; 
gills,  spiracle,  gill  rakers,  and  oper- 
cula,  tables,  271;  genital  system, 
tables,  266;  circulation  in,  tables, 
269;  central  nervous  system, 
tables,  275;  sense  organs  of, 
tables,  277;  integument  and  in- 
tegumentary sense  organs,  279; 
early  development  of,  tables,  280- 
281. 

Cklamydoselache,  antiquity  of,  10;  gill 
shields,  20;  lateral  line,  49,  50  (Fig. 
61);  C.  anguineus,  87  (Fig.  92); 
affinities  to  shark,  etc.,  96;  gill 
arches,  114. 

Chondrenchdys,  78;   anatomy  of,  85. 

CHONDROSTEI,  in  classification,  8, 
161,  162. 


Chondrosteus,  161,  162;  C.  acipense- 
roides,  161  (Fig.  165^). 

Chordates,  ancestors  of,  16  note;  de- 
scription of,  63-65. 

Christiceps,  eggs  of,  1 86. 

Circulatory  characters  in  Dipnoans, 
129. 

Cladodus,  teeth  of,  80  (Fig.  86^). 

Cladoselache,  in  classification,  8;  an- 
tiquity of,  9;  gill  slits,  16;  gill 
shields,  20;  dorsal  fins  of,  33  (Fig. 
41) ;  caudal  fin  of,  36,  37  (Fig.  46), 
38;  pectoral  and  ventral  fins  of,  42 
(Figs.  49,  50),  43-46;  a  primitive 
form  of,  78;  description  of,  79; 
anatomy  of,  79  (Figs.  86  and  86,4 
and  86.5);  dentition  of,  86;  affini- 
ties of,  95,  98  (Fig.  103);  gill 
arches,  114. 

Clark,  W.,  130,  133  note,  Frontispiece. 

Clasping  spine  of  Chimaeroids,  114; 
absence  of,  in  Dipnoans,  129. 

Claypole,  E.  W.,  66,  67,  71,  80,  130. 

Climatius,  anatomy  of,  82  (Fig.  89). 

Clupeoid,  antiquity  of,  9;  heart,  conus 
and  bulbus  arteriosus,  258  (Fig. 
320) ;  heart,  etc.,  comparison  tables 
of,  260. 

Coccosteus,  in  classification,  8;  locali- 
ties, 130;  anatomy  of  C.  detipiens, 
I3I~I33  (Figs.  130-132);  dermal 
and  ventral  plates  of,  132  (Figs. 
131,  132);  lateral  line  in,  135;  eyes 
of,  135- 

Cochliodonts,  86;   dental  evolution  of, 

112. 

Cod,  barbels  of,  46,  47  (Fig.  55 ), 
171;  description  of  Gadus  morrhua* 
174  (Fig.  182);  circulation  inr 
tables  of,  269. 

C&lacanthus,  in  classification,  8;  dor- 
sal fin  of,  33,  34  (Fig.  43),  43;  de- 
scription of,  87  (Fig.  92),  153;  as 
a  Crossopterygian,  147;  C.  elegans, 
153  (Fig.  155). 

Columbia  College  Museum,  130,  135,. 
Frontispiece. 

Conus  arteriosus,  comparison  tables  of,. 


INDEX 


289 


258  (Figs.  316-325),  260;  v.  Sharks, 
etc. 

Cope,  E.  D.,  8,  10;  phylogenetic 
table  of,  compared,  282. 

Cricotus,  54;   parietal  foramen  of,  54. 

CROSSOPTERYGII,  in  classification,  8; 
antiquity  of,  9;  unpaired  fins  of,  33 
(Fig.  43);  affinities  to  shark,  96; 
included  in  the  term  Ganoid,  139; 
ancestry  of,  147;  a  group  of  Teleo- 
stomes,  147;  description  of,  148- 
155  (Figs.  148-156,4);  habits  of 
living  and  breeding,  150;  fossil 
forms,  150-155  (Figs.  151-156^); 
pakeozic,  166  (Fig.  171  A}. 

Ctenodus,  in  classification,  8;  median 
foramen  of,  5  5 ;  affinity  to  Cerato- 
dust  122,  124;  ancestry  of,  147. 

Ctenolabrus  cceruleus,  larval  develop- 
ment of,  224  (Figs.  303-309),  225. 

Curves  of  fishes,  5,  6. 

Cusk,  barbels  of,  46,  47  (Fig.  55). 

Cusps,  v.  Derm  cusps. 

CYCLOSTOMES,  in  classification,  7,  8; 
antiquity  of,  9;  metamerism  in,  14- 
16;  gills  of,  18;  lampreys,  57-63; 
their  affinities^  63-65;  palaeichthyic 
affinities,  70;  eggs  and  breeding 
habits  of,  180,  181  (Figs.  186,  187); 
fertilization  of  eggs,  187  note;  larval 
development,  214,  215  (Figs.  212, 
215,  p.  189,  and  72,  p.  60) ;  names  of 
authors  and  works,  list  of,  234-238; 
skeleton  of,  tables,  252;  heart,  conus, 
and  bulbus  arteriosus,  tables,  260; 
gills,  spiracles,  gill  rakers,  and  oper- 
cula,  tables,  260;  digestive  tract, 
tables,  262  (Fig.  326),  263;  swim- 
bladder,  tables,  264;  genital  system, 
tables,  266;  urinogenital  ducts  and 
external  openings,  tables,  266,  267 
(Fig.  332) ;  abdominal  pores,  tables, 
271,  272  (Fig.  340);  central  ner- 
vous system,  tables,  274;  sense  or- 
gans, tables,  276;  integument  and 
integumentary  sense  organs,  tables, 
278. 

Cyprinodonts,  eggs  of,  185. 


Davidoff,  M.,  phylogenetic  table  of, 
compared,  283. 

Davis,  J.  W.,  84. 

Dean,  B.,  8,  78,  128,  132. 

Deep-sea  fishes,  lateral  line  in,  49. 

Defences,  v.  Dermal  and  Teeth. 

Dental  plate,  of  Sandalodus,  24  (Fig. 
28),  28;  of  sting-ray,  24  (Fig.  29); 
of  eagle-ray,  24  (Fig.  30),  27;  of 
Arthrodirans,  136,  137  (Figs.  138- 
144);  of  Dinichthys,  136-138. 

Denticle,  v.  Dermal  defences. 

Dentine,  v.  Shark,  skin  of. 

Derm  cusps,  origin  of,  30. 

Dermal  defences  of  fishes,  23-30;  of 
shark,  23,  24  (Figs.  30,  31);  evolu- 
tion of,  24  (Figs.  24-26),  25;  of 
Chimaeroids,  113;  of  Coccosteus  de- 
cipiens,  132  (Fig.  131);  v.  Fin 
spines. 

Dermal  sense  organs,  v.  Sensory  or- 
gans, integumentary. 

Development,  v.  Fishes,  Eggs,  larval, 
etc. ;  comparison  table  of  early,  280, 
281. 

Devil  ray  or  mantis,  v.  Dicerobatis. 

Dicerobatis,  95,  96  (Fig.  102^4). 

Digestive  tract,  comparison  tables  of, 
263  (Figs.  326-331). 

Dinichthys,  Frontispiece;  pineal  fun- 
nel>  55  >  general  description,  130- 
138;  type  specimens  in  Columbia 
College  Museum,  130  (Frontispiece 
and  Figs.  133-137);  fin  and  fin 
spine,  131;  D.  intermedius,  resto- 
ration of  by  Newberry,  133  (Fig. 
133  and  Frontispiece);  elater-joint 
of,  134;  dermal,  ventral,  and  pineal 
plates  of,  133  note;  dorsal  plates  in 
Columbia  College  Museum,  135; 
jaws  of,  136, 137  (Figs.  138-144);  in- 
ter movement  of  dental  plates  of,  1 38. 

Diphycercal-shaped   fin,  35,  37  (Fig. 

47). 
Diplognathus,  jaw  of,  136,  137  (Figs. 

141-143). 
Diplurus,  147,  153,154;   D.longicau- 

datus,  154  (Fig.  156). 


290 


INDEX 


DIPNOANS,  in  classification,  7,  8;  an- 
tiquity of,  9,  10,  147;  swim-bladder 
of,  21;  affinities  to  shark,  96,  98 
(Fig.  103);  general  description  of, 
116-129  (Figs.  121-129);  structural 
characters  and  general  anatomy  of, 
116-120  (Fig.  121);  skeleton  of, 
118  (Fig.  122),  119;  fossil  forms, 
120-124  (Figs.  123-126);  living 
forms,  123-127  (Figs.  127-129^); 
relationships,  127-129;  amphibian 
characters  of,  127,  129;  kinship  to 
sharks,  127;  the  advancing  struc- 
tures of,  1 29 ;  the  Arthrodiran  lung- 
fishes,  129-138  (Figs.  130-144); 
arthrodiran  affinities,  136;  eggs  and 
breeding  habits,  181  (Fig.  192), 
185;  larval  development  of,  218- 
221  (Figs.  290-295) ;  names  of 
authors  and  works  on,  list  of,  244- 
246;  comparison  tables  of  skeleton, 
253;  skeleton  of  Protopterus  annec- 
tans,  119  (Fig.  122);  skull  and 
branchial  arches,  table  of  relations 
of,  257;  heart,  conus  and  bulbus 
arteriosus,  tables  of,  258  (Figs.  320, 
321 );  comparison  tables  of  heart,  etc., 
260;  digestive  tract,  262  (Fig.  329)  ; 
comparison  tables  of  digestive  tract, 
263;  genital  system,  tables,  266; 
urinogenital  ducts  and  external 
openings,  tables,  267  (Figs.  332- 
337);  circulation  in,  tables,  269; 
brain,  272  (Fig.  343) ;  central  ner- 
vous system,  tables,  275;  sense  or- 
gans, tables,  277;  integument  and 
integumentary  sense  organs,  tables, 
279;  early  development  of,  compari- 
son tables,  280-281. 

Dipterus,  in  classification,  8;  antiquity 
of,  9;  description  of,  121  (Figs. 
123-125),  122. 

Dohrn,  A.,  40,  63. 

Dolphin,  fish-like  form  of,  6. 

Dorsal  fin,  v.  Fins. 

Drum-fish,  barbels  of,  46,  47  (Fig. 
56). 

Dugong,  fish-like  form  of,  6. 


Eagle-ray  {Myliobatis) ,  dental  plates 
of,  24  (Fig.  30),  27. 

Early  development,  v.  Development. 

Edestus  heinrichsii,  fin  spine  of,  28-30 
(Figs.  35-38). 

Edinburgh  Society,  Transactions  of, 
quoted,  70. 

Edwards,  V.  N.,  184. 

Eel,  movement  of,  2  (Fig.  2) ;  gills  of, 
18;  median  fins  of,  31;  description 
of  Anguilla  vulgar  is,  171,  173  (Fig. 
1 80). 

Eggs  of  fishes,  180-186  (Figs.  186- 
199)1  v-  Comparison  tables  of  the 
early  development  of  fishes,  280. 

ELASMOBRANCHII,  in  classification,  8, 
9;  antiquity  of,  9;  description  of, 
72-97  (Figs.  83-102);  affinities  of, 
95 ;  resemblances  to  lung-fishes,  1 28, 
129;  to  Athrodirans,  136,  v.  Shark; 
eggs  and  breeding  habits  of,  183, 
184  (Figs.  189,189^);  circulation 
in,  268  (Fig.  338),  269;  central  ner- 
vous system,  tables  of,  274,  275. 

Elonichthys,  156;  E.  (Rhabdolepis) 
macropterus,  156  (Fig.  158). 

Embiotocids,  eggs  of,  185. 

Emery,  C.,  169,  170. 

Enamel  of  shark  skin,  23,  24  (Fig. 
20) ;  enamel  organ  of  shark,  23,  24 
(Fig.  20). 

Entering  angle  of  fishes,  5,  6. 

Environment,  changes  due  to,  167- 
169  (Figs.  172-174). 

Erythrinus,  swim-bladder  of,  22  (Fig. 

15)- 
Eurynotus,     157;      E.  crenatus,     156 

(Fig.  159). 
Eusthenopteron.)   151—153;    E.  foordi, 

152  (Fig.  154). 
Evolution,  of  fishes,  slowness  of,  1 1 ; 

of  fins,  30-46;   of  unpaired  fins,  31- 

39  (Figs.  39-43)  ;  of  paired  fins,  39- 

46  (Figs.  49-54)- 
Excretory  system,  tables  of,  270,  271 

(Figs.  332-337,  P- 267). 
Exoskeletal     specializations    of    Dip- 

noans,  129. 


INDEX 


29I 


Eye,  v.  Pineal  eye. 

Feeling,  sense  of,  46-48. 

Fertilization  phenomena,  186,  187,  v. 
comparison  tables  of  the  early  devel- 
opment of  fishes,  280. 

Fierasfer,  169,  170;  F.  acus,  169  (Fig. 

175). 

Fins,  location  of,  3,  4;  evolution  of, 
30-46  (Figs.  39-54);  unpaired,  31- 
39  (Figs.  39-43);  dorsal  and  anal, 
31-35  (Figs-  39-43);  caudal,  35- 
39  (Figs.  44-48);  paired,  39-46 
(Figs.  49-54);  pectoral,  41-43  (Figs. 
49,  5T-54);  ventral,  41-43  (Fig. 
50);  of  Chimaeroids,  113;  primitive 
dermal,  31 ;  of  Cladoselache,  33  (Fig. 
41)  ;  of  Ccelacanthus,  34  (Fig.  43)  ; 
of  Crossopterygian  (Holopty chins)  t 

33  (Fig-  43)- 

Fin  spines,  23;  description  of,  28-30 
(Figs.  32-38)  ;  of  Acanthodian,  29 
(Fig.  32);  of  Hybodus,  29  (Fig. 
33)  ;  of  sting-ray,  28,  29  (Fig.  34) ; 
of  Edestzis  heinrichsii,  28,  29  (Figs. 
35-38);  of  Chimaeroids,  113. 

Fishes,  defined,  i;  movement  of,  I,  2 
(Figs,  i,  2);  type  of  swift  swim- 
ming fish,  3,  4  (Fig.  3) ;  balanced 
in  water,  i,  4;  symmetry  of,  4;  nu- 
merical lines  of,  5,  6  (Figs.  5-8); 
effect  of  environment  of,  7;  classifi- 
cation of,  7,  8;  geological  distribu- 
tion of,  9;  importance  of  group,  IO; 
permanence  of,  IO;  evolution  of,  II ; 
generalized,  1 2 ;  characteristic  struc- 
ture of,  14-56  (Figs.  9-60) ;  meta- 
merism, 14-16;  aquatic  breathing, 
gills,  etc.,  16-23  (Figs.  9-19);  der- 
mal defences  of,  23-30  (Figs.  20- 
38) ;  teeth  in  highly  modified  fishes, 
28;  development  of,  179-225  (Figs. 
186-309);  embryology  of,  1 79 ;  eggs 
and  breeding  habits  of,  180-186 
(Figs.  186-199);  fertilization  of 
eggs  of,  1 86,  187;  development  of 
eggs  of,  187-214  (Figs.  200-283); 
larval  development  of,  213-225 


(Figs.  284-309) ;  names  of  authors 
and  works,  on  the  general  subject, 
231-234;  skeletons,  table  of,  252, 
253  (Figs.  69,  84,  105,  122,  146, 
147,  and  310-315);  skull,  jaw,  and 
branchial  arches,  tables,  254  (Figs. 
310-315);  heart  of,  258  (Figs. 
316-325),  260;  comparison  tables 
of  heart  of,  260;  gills,  spiracles, 
gill  rakers,  and  opercula,  tables, 
259  (Figs.  9-12),  260,  261;  di- 
gestive tract,  tables,  262  (Figs.  326- 
331),  263;  swim-bladder,  tables, 
264,  265  (Figs.  13-19);  genital 
system,  tables,  266,  267  (Figs.  332- 
337);  circulation  in,  tables,  268 
(Fig.  338),  269;  excretory  system 
and  urinogenital  ducts,  270,  271 
(Figs.  332-337,  p.  267) ;  abdominal 
pores,  271 ;  brain  of,  272  (Figs.  339- 
341),  273  (Figs.  342-344);  central 
nervous  system,  tables,  274,  275; 
sense  organs,  tables  of,  276,  277; 
characters  of  integument  and  in- 
tegumentary sense  organs,  278, 
279;  early  development,  compari- 
son tables  of,  280,  281. 

Flounder,  171;  description  of,  174, 
175;  Pseudopleuronectes  america- 
nus,  172  (Fig.  183). 

Fossil  forms,  v.  Sharks,  Chimaeroids,  etc. 

Fraas,  157. 

Fric,  102,  119. 

Frilled  shark,  v.  Chlamydoselache,  etc. 

Fritsch,  A.,  42,  83. 

Gadoid,  9. 

Gadus,  v.  Cod. 

Gage,  S.,  182. 

Ganoid  plates,  in  jQLtheolepis,  24  (Fig. 
25);  in  Lepidosteus,  24  (Fig.  24); 
in  Callichthys,  24  (Fig.  26). 

GANOIDS,  in  classification,  8,  148;  an- 
tiquity of,  9;  dermal  plates,  24  (Fig. 
25),  25;  Ganoid  includes  the  Cros- 
sopterygians,  139  note;  the  term 
"  Ganoid  "  used  in  the  popular  sense 
to  denote  the  Teleostomes,  139;  con- 


292 


INDEX 


trasted  with  Teleost,  144  (Fig.  147) ; 
air-bladder  like  that  of  a  Dipnoan, 
145;  J.  Miiller  as  to  structural  differ- 
ences between  Ganoids  and  -Tele- 
osts,  145;  recent  Ganoids,  159; 
Mesozoic,  166  (Fig.  171  A);  eggs 
and  breeding  habits,  181  (Figs.  193, 
194);  fertilization  of  eggs  of,  187; 
development  of  eggs  of,  202-207 
(Figs.  249-268) ;  larval  development, 
211-223  (Figs.  296-302);  names  of 
authors  and  works  on,  246-249; 
skeleton,  tables  of,  253 ;  skeleton  of 
Polypterus  bichir,  144  (Fig.  147); 
digestive  tract,  tables,  262  (Figs. 
326-331);  urinogenital  ducts  and 
external  openings,  tables,  266,  267 
(Figs.  332-337) ;  abdominal  pores, 
tables,  271;  tables  of  early  devel- 
opment, 280,  281. 

Ganoine,  166  note. 

Carman,  87,  93,  109,  no. 

Gar-pike,  v.  Lepidosteus. 

Gegenbaur,  C.,  39,  40,  42,  146. 

Generalized  fishes,  defined,  12. 

Genital  system,  comparison  tables  of, 
266  (Figs.  332-337) ,  27°.  271- 

Geological  distribution  of  fishes,  9. 

Geologist,  American,  quoted,  80. 

Gill,  T.,  no;  phylogenetic  table  of, 
compared,  283. 

Gill  rakers,  20;  comparison  tables  of, 
260. 

Gill  shields,  20 ;  v.  Sharks,  Chimaeroids, 
etc. 

Gills,  16-23;  evolution  of,  18;  of 
Amphioxus,  16;  of  Bdellostoma,  17 
(Fig.  9);  of  Myxine,  17  (Fig.  10); 
of  shark,  17  (Fig.  n);  of  Teleost, 
17  (Fig.  12);  of  Cyclostomes,  18; 
of  Heptanchus,  1 6,  19;  of  mullet, 
20;  of  Brevoortia  (menhaden),  20; 
of  Selache,  20;  number  of  gill  slits, 
1 6,  note;  table  of  comparison  of, 
260,  261  (Figs.  9-12,  p.  259). 

Goette,  A.,  189. 

Goldfish,  170;  Carassius  auratus,  170 
(Fig.  176). 


Goode,  G.  B.,  3,  47,  89,  90, 92,  94,  95, 
103,  108,  155,  160,  162,  163,  171, 

1 73-1 77- 

Graf,  A.,  75,  102,  119. 
Greenland  shark,  v.  Lamargus. 
Guitel,  F.,  181. 
Gunn,  M.,  70. 
GUnther,  A.,  60,  90,  96,  103,  123,  125, 

146,  162,  168,  170,  172,   178,  181; 

phylogenetic    table    of,    compared, 

283. 

Gurnard,  v.  Prionotus. 
Gyroptychius,  150,  151  (Fig.  151). 

Haeckel,    146;     phylogenetic    table, 

compared,  282. 

Hagfish,  in  classification,  8;  v.  Myxine. 
Harriotta,  103,  104,  108  (Fig.  117); 

clasping  spine  of,  115. 
Heart,  v.  Sharks,  etc. 
HEMIBRANCHIATES,  176. 
HemitripttruS)    barbels    of,    46,    47 

(Fig.  57). 

Heptabranchias,  v.   Notidanus. 

Heptanchus,  v.  Notidanus. 

Hertwig,  O.,  54,  204. 

Heterocercal  caudal  fin,  35,  37  (Figs. 
45»46). 

HETEROSOMATA,  175. 

Hippocampus,  176;  H.  heptagonus, 
177  (Fig.  185)  ;  eggs  and  breeding 
habits,  1 86. 

Hofer,  B.,  24. 

Hoffman,  187  note. 

HOLOCEPHALI,  v.  Chmueroids;  heart, 
conus  and  bulbus  arteriosus,  tables, 
260;  digestive  tract,  tables,  263; 
swim-bladder,  tables,  264. 

Holoptychius,  in  classification,  8;  un- 
paired fins  of,  33  (Fig.  33) ;  ances- 
try of,  147;  description  of,  150;  H. 
andersoni,  151  (Fig.  153). 

Homocercal  caudal  fin,  35,  37  (Fig-48). 

Howes,  G.  B.,  42;  phylogenetic  table 
of,  compared,  282. 

Huxley,  131,  257. 

Hybodus,  number  of  gill  slits,  1 6  note; 
fin  spines  of,  28,  29  (Fig.  33). 


INDEX 


293 


Hydrolagus   colliei,   general   anatomy 

of,  100  (Fig.  104),  no. 
HYPERORARTIA,  62. 

ICHTHYOMI,  in  classification,  8. 

Innes,  W.,  149. 

Integument,  v.   Shark,  sense  organs, 

etc. 

Intestine,  v.  Digestive  tract. 
Ischyodus,  103  (Fig.  1 06) ;  mandibular 

of,  106  (Figs,  in,  112),  112. 

Jaekel,  O.,  92,  113. 

Janassa,  86. 

Jaws  of  fishes,  24,  27;  of  Port  Jackson 

shark,  24  (Fig.   27),  27;  table  of 

relations  of,    254  (Figs.  310-315), 

256,  257. 
Journal   of    Morphology,   quoted,    51 

note,  1 60. 

Kepler,  W.,  130. 

Klaatsch,  phylogenetic  table  of,  com- 
pared, 282. 
Kner,  82. 
Kreft,  125. 
Kupffer,  K.  v.,  187  note,  189,  222. 

Labrax  lineatus,  v.  Bass. 

Lczmargus,  shagreen  denticle  of,  24 
(Fig.  21),  25;  described,  90  (Fig. 
96  B*} ;  breeding  habits  of,  183  and 
note. 

Lagocephalus,  description  of  Z.  kzvi- 
gatus,  176  (184^). 

Lamna,  89,  90  (Fig.  96). 

Lamprey,  classified,  8;  metamerism 
in,  14-16;  gills  of,  17;  v.  Petromy- 
zon,  Cyclostomes,  etc. 

Lampreys,  v.  Cyclostomes,  etc.;  com- 
parison table  of  the  early  develop- 
ment of,  280,  281. 

Lankester,  E.  R.,  66. 

Larva,  v.  Fishes,  larval  development 
of. 

Lateral  line,  48-53  (Figs.  61-68);  of 
Chimaeroids  and  shark,  114;  in  Coc- 
costeus,  135. 


Lepidosiren,  in  classification,  8;  swim- 
bladder  of,  22  (Fig.  1 8);  account 
of,  125  (Fig.  129),  126;  swim- 
bladder,  tables  of,  264,  265  (Fig. 
18). 

Lepidosteus,  in  classification,  8;  an- 
tiquity of,  9,  1 66  (Fig.  171  A}\ 
swim-bladder  of,  21,  22  (Fig.  14); 
ganoid  dermal  plates  of,  24,  25  (Fig. 
24) ;  especial  interest  of  gar-pike  in 
connecting  the  Ganoids  with  the 
Crossopterygians,  159;  gar-pike,  Z. 
platystom  us,  described ,  1 5  9- 1 60  (  Fig. 
I57);  eggs  and  breeding  habits  of, 
181  (Fig.  193),  185;  fertilization 
of,  187;  development  of  egg  of,  203 
(Figs.  265-268),  207;  heart,  conus 
and  bulbus  arteriosus,  258  (Fig. 
322);  comparison  tables  of  heart, 
etc.,  260;  gills,  spiracle,  gill  rakers, 
and  opercula,  tables,  261 ;  digestive 
tract,  tables,  263;  swim-bladder, 
tables,  264,  265  (Fig.  14);  genital 
system,  tables,  266;  excretory  sys- 
tem and  urinogenital  ducts,  271. 

Leptolepis,  165;  Z.  sprattiformis,  165 
(Fig.  170). 

Leydig,  F.,  51  note. 

Limb  structure  in  Dipnoans,  129. 

List  of  names  of  authors  and  of  their 
works,  231-251. 

List  of  the  derivations  of  proper 
names,  227-230. 

LOPHOBRANCHII,  1 66  (Fig.  171  A}, 
178. 

Lung-fishes,  v.  Dipnoans. 

Lungs,  v.  Swim-bladder. 

Mackerel  shark,  v.  Lamna. 

Mackerel,  Spanish,  movement  and  fins 
of,  2,  3  (Fig.  3);  front  view  of,  4 
(Fig.  4);  lines  of,  5  (Fig.  6). 

Macropetalichthys,  eyes  of,  135. 

Manatee,  fish-like  form  of,  6. 

Mandibles  of  Chimseroids,  113;  articu- 
lation of  in  Dipnoans,  129. 

Mantis,  or  devil-ray,  v.  Dicerobatis. 

Marey,  2. 


294 


INDEX 


MARSIPOBRANCHS,    v.     Cyclostomes ; 

tables  of  the  early  development  of, 

280,  281. 
McClure,  182. 
Mechanical   adaptation   of   the    fish's 

form,  5>  6. 

Median  fins,  v.  Fins. 
Megalurus,    165;    M.   elegantissimus, 

165  (Fig.  171). 
Megaptera,  v.  Whale;  M.  longimana, 

numerical  lines  of,  5  (Fig.  7),  61. 
Menaspis,  skin  defences  of,  113. 
Menhaden,  v.  Brevootia. 
Metamerism,  vertebrate,  of  fishes,  14- 

16;  of  lampreys,  15;  of  sharks,  16. 
Miall,  L.,  126. 
Microdon,    157;    M.    wagneri,    158 

(Fig.  163). 
Mivart,  St.  G.,  40 
Modern  fishes,  v.  Teleostomes. 
Mollier,  S.,  39. 
Monk-fish,  v.  Rhina. 
Mormyrus,  171,  172;  M.  oxyrhynchus, 

172  (Fig.  179). 
Morphology,   Journal   of,  quoted,    51 

note. 
Mouth  of  fishes,  v.  Jaws,  Teeth,  etc. ; 

of  catfish  (a  Teleostome),  64  note. 
Movement  in  water,  I,  2  (Figs,  i  and 

2). 

Mucous  canal  system,  v.  Lateral  line. 

Miiller,  Johannes,  145. 

Mullet,  gills  of,  20. 

Murtena,  173. 

Myliobatis,  v.  Eagle-ray. 

Mylostomids,'\T\  classification,  8;  trunk 
of,  136;  jaws  of  Mylostoma  varia- 
bilis,  136,  137  (Fig.  138). 

Myriacanthus,  in  classification,  8  ; 
restoration  of,  104;  head  region  of, 
105  (Fig.  106) ;  dermal  plates  of 
head  and  snout,  105  (Figs.  106, 
A  and  B),  113;  mandibular,  106 
(Fig.  107);  dorsal  spine,  107  (Fig. 
114);  dental  evolution,  112;  sha- 
green tubercles  and  dermal  bones 
and  plates,  105  (Fig.  106),  107 
(Fig.  114),  113. 


Myxine,  classification,  8;  gills  of,  17 
(Fig.  10),  18;  general  description, 
of  M.  glutinosa,  59,  60  (Fig.  71), 
61  (Fig.  72  j£);  eggs  of,  180-182 
(Fig.  187);  genital  system,  tables 
of,  266;  excretory  system  and  urino- 
genital  ducts,  270. 

Myxinoid,  Californian,  gills  of,  18; 
teeth  of,  57;  eggs  of,  182  (Figs.  186 
A  and  187  A}  ;  comparison  tables 
of  the  early  development,  280,  281. 

Names,    list     of    authors    and    their 

works,  231-251. 

Names,  list  of  derivations  of,  227-230. 
Nares,  in  Dipnoans,  129. 
Natterer,  J.,  125. 
Necturus,  swim-bladder  of,  21. 
Nervous   system,   central,    272   (Figs. 

339-340!    273    (Figs.    342-344), 

274,  275. 
Newberry,  J.  W.,   78,   106,   120,  130, 

131,  132,  136. 
Newton,  106. 
Nicholson,  H.  A.,  125. 
Notacanthns  sexspinis,  168  (Fig.  174). 
Notidanus,  antiquity  of,  9;    gill  slits, 

1  6,   19;    pectoral   fin,   40-42    (Fig. 

52),  44,  45;   described,  87-89  (Fig. 

93);   affinities,  96;   skull,  jaws,  and 

branchial     arches     of,     254    (Fig. 


Numerical  lines  of  fishes,  5,  6  (Figs. 
5-8). 

Onychodus,  in  classification,  8. 
Operculum  of  Teleosts,  19;  comparison 

tables  of,  260. 
Ophidium,   barbels   of,   46,   47    (Fig. 

55)- 

Opisthure,  in. 

Osteolepis,  in  classification,  8;  descrip- 
tion of,  150,  ^51  (Fig.  152). 

OSTRACODERMS,  classified,  8;  antiquity 
of,  9;  description  of,  65-71;  types 
of,  67;  affinities  of,  66  (Fig.  77), 
70;  list  of  authors  and  works  on 
Ostracoderms,  238. 


INDEX 


295 


Paddle-fish,  v.  Polyodon. 

Palaaspis  americana,  67  (Fig.  75) ; 
paired  fins  or  spines,  71  note. 

Paltzdaphus,  median  foramen,  55. 

Palaoniscus,  in  classification,  157,  158 
(Fig.  164);  Palseozic,  166  (Fig. 
171,4). 

Palaospondylus,  in  classification,  8; 
antiquity  of,  9,  71 ;  P.  gunni,  65 
(Fig.  73),  70;  palseichthyic  affini- 
ties, 70;  list  of  authors  and  their 
works  on  Pal&ospondylus,  238. 

Pander,  121,  151. 

Paraliparis  bathybius,  1 68  (Fig.  172). 

Parexus,  pectoral  tin  of,  42  (Fig.  51), 

44- 

Parker,  W.  N.,  7,  117,  127,  128. 
— ,  T.  J.,  41,  58. 

Parsons,  5,  6. 

Perca,  v.  Perch. 

Perch,  antiquity  of,  9;  scales  of,  25 
(Fig.  31  A},  26,  171;  described, 
174;  Perca  americana  (=  fltivia- 
talis?},  173  (Fig.  181);  digestive 
tract,  tables  of,  262  (Figs.  326-331). 

Petalodonts,  86. 

Petromyzon,  61 ;  P.  marinus,  60  (Fig. 
72),  61  (Fig.  Z>),  62;  skeleton  of, 
58  (Fig.  69);  eggs  of,  180-183; 
eggs  of  P.  marinus,  181  (Fig. 
188);  fertilization  of  eggs,  187; 
development  of,  188-192;  develop- 
ment of  P.  planeri,  189  (Figs.  200- 
214);  digestive  tract,  tables  of,  262 
(Fig.  326) ;  genital  system,  tables 
of,  266;  urinogenital  ducts  and  ex- 
ternal openings,  267  (Fig.  332); 
excretory  system  and  urinogenital 
ducts,  270 ;  brain  of,  272  (Fig. 
340) ;  central  nervous  system,  274. 

Phaneropleuron,  in  classification,  8; 
description  of,  122  (Fig.  126). 

Phoctzna  lineata,  v.  Porpoise. 

Phylogeny,  tables  of,  98  (Fig.  103), 
166  (Fig.  171  A}\  comparison  of 
the  phylogenetic  tables  of  the  differ- 
ent authors,  282,  283. 

Phyllopteryx,  178. 


PHYSOSTOME,  166  (171  A). 

Pineal  eye,  53-56. 

Pipe-fish,  v.  Syngnathus. 

PISCES,  v.  Fishes. 

PLECTOGNATHI,  176. 

Pleuracanthus,  in  classification,  8; 
gill  slits,  16;  a  fossil  shark,  78; 
anatomy  and  skeleton  of,  83  (Fig. 
90);  dermal  bones  of  head  roof, 
84  (Fig.  90  A) ;  teeth  of,  84  (Fig. 
90  .5);  affinities  of,  95,  98  (Fig. 
103);  anterior  spine  of  dorsal  fin, 
114;  tail  of,  115;  Coccosteus  com- 
pared with,  131. 

PLEUROPTERYGII,  in  classification,  8. 

Pogonias,  v.  Drum-fish. 

Pollard,  H.  B.,  64,  113,  132. 

Polyodon,  barbels  of,  46,  47  (Fig.  59), 
48;  described,  160-163;  P.  spatula, 
162  (Fig.  1 66.5);  gills,  spiracle, 
gill  rakers,  and  opercula,  tables  of, 
261. 

Poly  pier  us,  swim-bladder  of,  21,  22 
(Fig.  17) ;  origin  of  derm  cusps,  30; 
caudal  fin  of,  36,  37  (Fig.  47) ;  tail 
of,  115;  skeleton  of  P.  bichir,  144, 

147  (Fig.    147) ;     contrasted   with 
Teleosts,  144;   P.  bichir  described, 

148  (Fig.   148),  149  note;  P.  lap- 
radei,  149  (Fig.    149);   in  table  of 
phylogeny,  166  (Fig.  171^);  skull 
and    branchial    arches,    254    (Fig. 
314) ;   table  of  relations  of  skull  and 
branchial  arches,  257;    comparison 
tables  of  gills,  spiracle,  gill  rakers, 
and  opercula,  261 ;    digestive  tract, 
tables,   263;    swim-bladder,   tables, 
264, 265  (Fig.  1 7)  ;  excretory  system 
and  urinogenital  ducts,  tables,  270. 

i  Porcupine-fish,  v.  Chilomycterus. 
!  Porpoise,  striped,  lines  of,  5  (Fig.  5). 
Port  Jackson  shark,  v.  Cestracion. 
Powrie,  82. 
Prionotus,  barbels  of,  46,  47  (Fig.  60), 

48. 

Pristiophorus,  antiquity  of,  9 ;  descrip- 
tion of,  92  (Fig.  99) ;  affinities  of, 
96-98  (Fig.  103). 


296 


INDEX 


Pristis,  antiquity  of,  9;  description  of, 
91  (Figs.  98  and  98^4);  affinities 
of,  96-98  (Fig.  103). 

Pristiurus,  larval  development  of,  215, 
216  (Fig.  284). 

Protocercy,  35. 

Protopterus,  swim-bladder  of,  22  (Fig. 
18);  anatomy  of,  116  (Fig.  121); 
paired  fin  structure,  118  (Fig.  122), 
119;  jaws  and  skull,  119  (Fig. 
122  A};  account  of,  126  (Fig. 
129^);  Coccosteus  compared  with, 
131;  heart,  conus  and  bulbus  arte- 
riosus,  285  (Fig.  325) ;  comparison 
tables  of  heart,  etc.,  260 ;  gills, 
spiracle,  gill  rakers,  and  opercula, 
tables,  261;  digestive  tract,  tables, 
262  (Fig.  329),  263;  swim-bladder, 
tables,  264,  265  (Fig.  18);  circula- 
tion in,  tables,  269;  excretory  sys- 
tem and  urinogenital  ducts,  270; 
abdominal  pores,  271;  brain  of,  273 
(Fig.  343) ;  central  nervous  system 
tables,  275. 

Psammodus,  dentition,  86. 

Psephurus,  160-163;  P-  gladius,  162 
(Fig.  166,4). 

Pseudopleuronectes,  v.  Flounder. 

Pteraspis,  antiquity  of,  9;  described, 
67  (Figs.  74,  76,  77). 

Pterichthys,  antiquity  of,  9;  described, 
69  (Figs.  80-82) ;  Arthrodira  associ- 
ated with  by  Traquair,  1 30. 

Putnam,  182. 

Pycnodont,  157,  158. 

Rabbit-fish,  v.  Lagocephalus. 

Rabl,  C.,  146;  phylogenetic  table  of, 
compared,  283. 

Raja,  v.  Ray. 

Rat-fish,  v.  Chimcera. 

RAY,  in  classification,  8;  antiquity  of, 
9;  shagreen  of,  24  (Fig.  23);  de- 
scription of,  93-95  (Figs.  100-102) ; 
barn-door  skate  (^?.  Icevis},  94  (Fig. 
101):  affinities,  95,  96,  98  (Fig. 
I03) ;  eggs  and  breeding  habits,  181 
(Fig.  189,4),  183,  184. 


Recent  sharks,  v.  Sharks. 

Relationships,  v.  Affinities,  under  the 
family  and  species. 

Respiration,  v.  Aquatic  breathing. 

Retzius,  G.,  phylogenetic  table  of,  com- 
pared, 282. 

Rhina,  91  (Fig.  97);  affinities  to 
shark,  96,  98  (Fig.  103) ;  brain  of, 
tables  of,  272  (Fig.  341). 

Rhinobatus,  antiquity  of,  9;  descrip- 
tion of,  93  (Fig.  100) ;  affinities  to 
shark,  98  (Fig.  103). 

Rhyncodus,  mandibular  of,  106  (Fig. 
in),  in. 

Ruckert,  J.,  187. 

Ryder,  J.  A.,  31,  37,  115. 

Salensky,  W.,  214  note. 

Salmonid,  antiquity  of,  9;  eggs  and 
breeding  habits,  186;  skull  and 
branchial  arches,  table  of,  254  (Fig. 
3i5)i  257. 

Sandalodus,  dental  plates  of,  24  (Fig. 
28),  28. 

Scales,  23;  of  Teleost,  24  (Fig.  31); 
degeneration  of,  26. 

Scaphaspis,  66  (Fig.  77),  67. 

Scaphirhynchus,  160;  S.  platyrhyncus, 
162  (Fig.  1 66). 

Scomberomorus  maculatus,  2,  3  (Fig. 
3)  ;  front  view  of,  4  (Fig.  4)  ;  lines 
of,  5  (Fig.  6). 

Sculpin,  barbels  of,  46,  47  (Fig.  57). 

Scyllium,  shagreen  of,  24  (Fig.  22), 
25>  90;  eggs  of,  181  (Fig.  189), 
183,  184  and  note;  development  of 
egg  of,  193  (Figs.  216-230);  larvae 
of,  215,  216  (Figs.  285-287);  skull, 
jaw,  and  branchial  arches  of,  254 
(Fig.  310),  256. 

Sea-bass,  v.  Serranus. 

Sea-cat,  v.  ChinHzra  and  Callorhyn* 
chus. 

Sea-horse,  v.  Hippocampus. 

Sea-raven,  v.  Hemitripterus. 

Sea-robin,  v.  Prionotus. 

Seal,  fish-like  form  of,  6. 

Selache,  gills  of,  20. 


INDEX 


297 


SELACHII,  in  classification,  8. 
Semionotus,  157;   S.  kapjfi,  157  (Fig. 

161). 

Semon,  R.,  125,  181,  199,  200,  219. 
Sense   organs,  characters   of,  46—56; 

tables  of,  276-277;  integument  and 

integumentary  sense  organs,  tables 

of,  278,  279. 
Sense  of  feeling,  46-48. 
Sensory  canals  in  head  of  Chimaera, 

3°- 

Sensory  tubules,  v.  Lateral  line. 

Serranus,  eggs  of,  181  (Fig.  196),  186; 
development  of  egg  of  S.  atrarius, 
208  (Figs.  269-283). 

Shad,  v.  Alosa. 

Shagreen  denticle  of  shark,  23-25 
(Figs.  20-22) ;  of  sting-ray,  24  (Fig. 
23),  25. 

SHARKS,  movement  of,  2;  in  classifi- 
cation, 7,  8;  antiquity  of,  9,  10,  72; 
gills  of,  17  (Fig.  n),  19;  spiracle 
of,  19;  gill  shields  of,  20 ;  skin, 
enamel,  and  dermal  denticle  of,  23- 
26  (Figs.  20-22) ;  shagreen  denticle 
of  the  Greenland  shark  (Ltsmargus), 
24  (Fig.  21);  jaw  of  Port  Jackson 
shark  (Cestracimf)^  24  (Fig.  27), 
27;  evolution  of  the  dermal  armour- 
ing, 25,  26  (Figs.  25,  26) ;  unpaired 
fins  of,  33,  34  (Figs.  39-43) ;  caudal 
fin  of,  36-39  (Figs.  45-47)  J  lateral 
line  of,  49,  50  (Figs.  6 1,  62),  51,  76; 
description  of,  72-98  (Figs.  83-103) ; 
position  of,  72;  general  anatomy  of, 
73  (Fig.  83);  skeleton  of,  74-76 
(Fig.  84);  sub-notochordal  rod  in 
skeleton,  76  (Fig.  85);  integument 
of,  76;  brain  of,  76;  nasal  organ, 
eye,  and  ear,  76;  renal  and  repro- 
ductive system  of,  76;  digestive 
tube,  viscera,  77;  heart,  77;  clasp- 
ers,  77;  fossil  sharks  described,  77- 
86  (Figs.  86-91) ;  teeth  of  fossil,  86; 
recent  sharks,  87-95  (Figs.  92-101)  ; 
affinities  of,  95-98  (Fig.  103) ;  eggs 
and  breeding  habits,  181  (Figs.  189- 
190),  183,  184;  fertilization  of  eggo, 


187  note;  development  of  egg  of, 
194-198  (Figs.  216-230);  larval  de- 
velopment of,  215-218  (Figs.  284- 
289);  list  of  authors  and  their  works 
on  sharks,  238-244;  comparison 
tables  of  the  skeleton  of,  252;  skel- 
eton of  Cestracion  galeatus,  75  (Fig. 
84),  255;  skull,  jaws,  and  branchial 
arches,  tables,  256;  heart,  tables, 
258  (Fig.  317),  260;  gills,  spiracle, 
gill  rakers,  and  opercula,  tables,  262 
(Fig.  u,  p.  259);  swim-bladder, 
tables,  264;  genital  system,  tables, 
266;  urinogenital  ducts  and  exter- 
nal openings,  267  (Fig.  333),  and 
tables,  270;  plan  of  circulation  in, 
tables,  268  (Fig.  338),  269;  ab- 
dominal pores,  tables,  271;  brain  of, 
272  (Fig.  341);  sense  organs  of, 
tables,  276;  integument  and  integ- 
umentary sense  organs,  tables,  279; 
comparison  tables  of  the  early  devel- 
opment of,  280,  281. 

Siluroid,  antiquity  of,  9;  affinity  and 
phylogeny  of,  147,  166  (171  A}, 
171;  South  American  Siluroid  {Cal- 
lichthys  armatus),  172  (Fig.  178); 
eggs  and  breeding  habits  of,  181 
(Fig.  195),  185,  186  and  note; 
heart,  conus  and  bulbus  arteriosus, 
tables  of,  258  (Fig.  318). 

Siphostoma,  eggs  and  breeding  habits 
of,  1 86. 

SIRENOIDEI,  in  classification,  8. 

Skates,  description  of,  93-95  (Figs. 
100-102)  v.  Ray. 

Skeleton,  v.  Shark,  Pleur acanthus,  Chi- 
mseroid,  Dipnoan,  Ceratodus,  etc. 

Skin  defences,  v.  Dermal  and  Teeth. 

Skull  of  fishes,  dermal  bones  of  head 
root  of  Pleuracanthus,  84  (Fig.  90 
A}-,  of  Chimaeroids,  113;  resem- 
blances of  skull  of  lung-fishes  to 
Elasmobranchs,  128;  of  Dinichthys 
intermedius,  133  (Fig.  133  and  Fron- 
tispiece) ;  table  of  relations  of  skull, 
jaws,  and  branchial  arches  of,  254 
(Figs.  310-315),  256. 


298 


INDEX 


Smithsonian  Institution,  Heptanchus, 
88  (Fig.  93). 

Solenostoma,  eggs  and  breeding  habits, 
1 86. 

South  American  lung-fish,  v.  Lepido- 
siren. 

South  American  Siluroid,  v.  Callichthys. 

Spatularia,  v.  Polyodon. 

Specialized  fishes,  defined,  12. 

Spines,  23;  v.  Fin  spines,  Clasping 
spines. 

Spiracle  of  shark,  18;  comparison 
tables  of,  260. 

Spook-fish,  v.  Chimsera  and  Chimae- 
roids. 

Spoon-bill  sturgeon,  v.  Polyodon. 

Squaloraja,  in  classification,  8;  affini- 
ties of,  98  (Fig.  103) ;  restoration  of, 
104,  105  (Fig.  io6,4);  mandibular 
of,  106  (Fig.  108) ;  frontal  spine  of, 
107  (Fig.  115);  dental  evolution  of, 
112;  skin  defences  of,  113. 

Sgualus,  89  (Fig.  94). 

Squatina,  v.  Rhina. 

Steindachner,  F.,  149,  150. 

Sticklebacks,  v.  Hemibranchiates. 

Sting-ray,  shagreen  of,  24  (Fig.  23); 
dental  plates  of  jaw,  24  (Fig.  29), 
25;  fin  spine  of,  28,  29  (Fig.  34). 

Stomach,  v.  Digestive  tract. 

Strong,  O.  S.,  112. 

Structure,  characteristic,  of  fishes,  14. 

Sturgeon,  v.  Acipenser ;  spoon-bill 
sturgeon,  v.  Polyodon  and  Psephu- 
rus ;  shovel-nose  sturgeon,  v.  Sea- 
phirhyncus ;  a  Liassic  sturgeon, 
v.  Chondrosteus. 

Swim-bladder,  hydrostatic,  I,  21,  22 
(Figs.  13-19);  of  Amia,  21,  22 
(Fig.  14);  of  gar-pike,  21,  22  (Fig. 
14)  ;  of  Dipnoans,  21 ;  of  Polypterus 
and  Calamoichthys,  21 , 22  (Fig.  17) ; 
of  Necturus,  21;  of  sturgeon,  22 
(Fig.  13)  ;  of  Teleosts,  22  (Fig.  13)  ; 
of  Erythrinus,  22  (Fig.  15);  of 
Ceratodus,  22  (Fig.  1 6);  of  Lepido- 
siren,  22  (Fig.  1 8);  of  Protopterus, 
22  (Fig.  1 8) ;  of  Dipnoans,  129 ; 


compared  with  reptiles,  birds,  and 
mammals,  20  (Fig.  19);  comparison 
tables,  264,  265  (Figs.  13-19). 

Swimming:  eel,  shark,  mackerel,  2. 

Symmetry  of  fishes,  4. 

Synechodus,  dentition  of,  86. 

Syngnalhus,  1 66  (Fig.  171  A]  ;  de- 
scription of,  177,  178;  S.  acus,  178 
(Fig.  185  A}\  eggs  and  breeding 
habits  of,  186. 

Tail,  v.  Caudal  fins. 

Teeth,  general,  23,  24  (Figs.  27-30) ; 
description  and  evolution  of,  27,  28; 
of  Port  Jackson  shark,  24  (Fig.  27), 
27,  86;  of  highly  modified  fishes, 
28;  of  Myxinoids,  57;  of  Cladodus, 
80  (Fig.  86  B} ;  of  Acanthodopsis, 
82  (Fig.  88  A} ;  of  Pleur acanthus, 
84  (Fig.  90  B} ;  of  fossil  sharks,  86; 
of  Chimseroids,  113;  resemblances 
of  lung-fishes  to  Elasmobranchs  as 
to  teeth,  128. 

TELEOCEPHALI,  included  in  Actinop- 
terygians,  8,  148;  description  and 
phylogeny  of,  165,  166  (Fig.  171  A). 

TELEOST,  antiquity  of,  9,  147;  gills  of, 
17  (Fig.  12),  19;  operculum  of,  19; 
gill  rakers  of,  20;  swim-bladder  of, 
22  (Fig.  13)  ;  swim-bladder  of  Ery- 
thrinus,  22  (Fig.  15);  scales  of,  24 
(Fig.  31);  caudal  fin  of,  36,  37 
(Fig.  48) ;  the  term  "  Teleost "  used 
in  the  popular  sense  to  denote  the 
modern  "  bony  fish,"  139;  the  perch 
a  convenient  type,  139;  general 
anatomy  of,  141-145  (Figs.  145, 
146) ;  skeleton  of  Percafluviatilis, 
142  (Fig.  146) ;  relationship  and 
descent,  145-147;  description  and 
phylogeny  of,  165, 166  (Fig.  171  A)\ 
modified  conditions  of,  167-171; 
eggs  and  breeding  habits,  181  (Figs. 
196-199),  185,  186;  fertilization  of, 
187  and  note;  development  of  egg, 
207-212  (Figs.  269-283)  ;  larval 
development,  223-225  (Figs.  303- 
309);  list  of  authors  and  their 


INDEX 


299 


works,  249-251;  comparison  tables 
of  the  skeleton  of,  253;  heart,  conus 
and  bulbus  arteriosus,  tables,  258 
(Figs.  324,  325),  260;  digestive  tract, 
tables,  262  (Fig.  331),  263;  urino- 
genital  ducts  and  external  openings, 
267  (Fig.  337),  and  tables,  271; 
circulation  in,  tables,  269;  abdomi- 
nal pores,  tables,  271;  brain  of,  273 
(Fig.  344) ;  central  nervous  system, 
tables,  275;  comparison  table  of  the 
early  development  of,  280,  281. 

TELEOSTOMES,  in  classification,  7,  8; 
antiquity  of,  9,  IO;  mouth  of,  64 
note;  opercular  apparatus  of,  114; 
tail  of,  1 1 5 ;  affinities  to  Arthrodirans, 
^36;  general  description  of,  139- 
178  (Figs.  145-185  A);  skeleton 
of,  141-143  (Fig.  146);  visceral 
parts  of,  143;  contrasted  with 
Ganoids,  144  (  Fig.  147) ;  Teleosts 
and  Ganoids  merged  into  one  group 
by  Prof.  Owen,  146;  descent  of, 
146;  affinities  with  the  Dipnoans 
generally  admitted,  146;  Rabl  de- 
rives them  from  a  selachian  stem, 
146;  Beard  and  Woodward  as  to 
their  descent,  146;  two  principal 
subdivisions  of,  147;  phylogeny, 
scheme  of,  165,  166  (Fig.  171  A)-, 
comparison  tables  of  skeleton  of, 
253 ;  table  of  relation  of  skull,  jaws, 
and  branchial  arches,  257;  heart, 
conus  and  bulbus  arteriosus,  tables, 
260;  gills,  spiracle,  gill  rakers,  and 
opercula,  tables,  261 ;  digestive 
tract,  tables,  263;  swim-bladder, 
tables,  264,  265  (Fig.  13);  genital 
system,  tables,  266;  sense  organs, 
tables,  277;  integument  and  integu- 
mentary sense  organs,  tables,  279. 

Telescope-fish,  v.  Carassiits. 

Terrell,  J.,  130. 

Thacher,  J.,  40. 

Thiolliere,  58. 

Thrasher  shark,  v.  Alopias. 

Tissues,  cellular  elements  of,  in  Dip- 
noans, 129.  .  . 


Titanichthys,  pineal  foramen  of,  55, 
56,  135;  size  and  localities  of,  130; 
lip-like  mandibles  of,  136;  mandi- 
bles of  T.  clarki,  136,  137  (Fig. 

139). 

Torpedo,  95  (Fig.  102). 
Trachosteus,  jaws  of,   136,   137  (Fig. 

140). 
Transactions   of    Edinburgh    Society, 

quoted,  70. 
Traquair,  R.   H.,  65,  68,  70,  71,  78,. 

128,  130,  132,  156,  157,  159. 
Trygon,    dental  plates  of  jaw  of,  24 

(Fig.  29);  fin  spine  of,  28,  29  (Fig. 

34). 
Turner,  W.,  217. 

Undina,  147,  153;  U.  gulo,  154 
(Fig.  156.4). 

United  States  Fish  Commission  Re- 
ports, quoted,  3,  89,  90,  92,  94,  95, 
155,  160,  162,  163,  171,  173-177. 

United  States  National  Museum,  Pro- 
ceedings of,  quoted,  103. 

Urinogenital  system,  comparison  tables 
of,  266,  267  (Figs.  332-337)>  27°» 
271. 

Urogymnus,  shagreen  of,  24  (Fig.  23). 

Ventral  plates  of  Coccosttus  decipiens^ 
132  (Fig.  132). 

Vertebral  axis  of  lung-fishes,  resem- 
blance to  Elasmobranchs,  128. 

Vienna  collection,  149  note. 

Visceral  characters,  resemblance  be- 
tween lung- fishes  and  Elasmo- 
branchs, 128;  of  Teleost,  143;  of 
Ganoids,  145. 

Walcott,  65. 

Ward,  H.  A.,  75. 

Whale,  fish-like  form  of,  6. 

Whale,  humpback,  numerical  lines  of, 

5  (Fig-  7)- 
Whiteaves,  152. 
Whitman,  C.  O.,  187  note. 
Wiedersheim,  R.,  40,  113. 
Willey,  A.,  16. 


300 


INDEX 


Wilson,  H.  V.,  208. 

Woodward,  A.  S.,  8,  10,  24,  25,  33, 
42,  66,  68-71,  80,  81,  106,  107, 
112,  121,  127,  129,  131,  132,  135, 
136,  146,  151,  154,  161,  164,  165; 
phylogenetic  table,  compared,  282. 

Works  on  the  general  subject,  fishes, 
231-234;  on  the  Cyclostomes,  234- 
238 ;  on  the  Ostracoderms  and 
Palaosp.ondylm,  238 ;  on  the  sharks, 
238-244;  on  the  Chimgeroids,  244; 
on  the  lung-fishes,  244-246;  on  the 


Ganoids,  246-249;   on  the  Teleosts, 
249-251. 

Xenacanthus,  pectoral  fin  of,  39,  40, 
42  (Fig.  53),  45;  v.  Pleuracan- 
thus. 

Zittel,  K.  v.,  table  of  geological  dis- 
tribution of  fishes,  9;  quoted,  81, 
82,  104,  124,  157,  158,  164,  165. 

Zoological  Society,  Proceedings  of, 
257  note. 


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TO 

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1  MONTH 


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FORM  NO.  PD8. 


BERKELEY,  CA 


